A PDF research report tracking and tracing method and device based on dark watermark

Abstract

The present invention discloses a method and device for tracking and tracing the source of a PDF research report based on a dark watermark. The method comprises the following steps: obtaining a PDF document of the original research report; slicing the watermark information to be added, and determining the watermark information to be added to each page according to the watermark information to be added and the number of pages of the PDF document of the original research report; encrypting the sliced watermark information; adjusting the distribution position of the watermark information on each page of the PDF document in a random or pseudo-random manner; and adding the encrypted watermark to the PDF document according to the distribution position. Accurate tracking and tracing is achieved by slicing the watermark information itself. The watermark information is encrypted, and a dynamic adjustment strategy for the watermark position is introduced. By changing the specific position of the watermark on each page of the PDF document in a random or pseudo-random manner, the difficulty of identifying and erasing the watermark is increased, and the concealment and durability of the watermark are enhanced.

Description

Technical Field

[0001] The present invention relates to the field of electronic information technology, and more specifically, to a method and device for tracking and tracing PDF research reports based on dark watermarks. Background Art

[0002] In today's society, the piracy and infringement of digital products are becoming increasingly serious, raising concerns about digital copyright protection and increasing the need for accurate tracking of leaked information. In the FinTech sector, research reports, as a crucial digital asset, are crucial for their security and traceability. When a user opens a research report in PDF format within a business system, the system embeds a unique watermark based on the user's personal characteristics. This ensures that if a PDF version of the research report is illegally leaked, the embedded watermark can be analyzed to trace and identify the source of the leak.

[0003] Current tracking technologies for research report PDFs primarily rely on watermarking algorithms. One method directly overlays a watermark in the form of an image generated from visitor information onto the PDF document; another method converts the PDF document into a series of images and then adds a watermark containing the visitor's personal information to these images. Both methods can help companies quickly identify potential culprits in the event of a document leak, thereby strengthening management and mitigating the risks associated with information leakage.

[0004] However, with the rapid development of information technology, traditional watermarking technology has demonstrated its limitations. For example, while visible watermarks embedded in PDF documents can serve as a preliminary copyright notice, modern image processing software can easily remove these markings, even after the document itself has been converted to an image format. Furthermore, advanced AI technology has made the removal of these markings more efficient and convenient. Furthermore, even with the more concealed dark watermarking technology, its protection capabilities are not indestructible. If a document lacks additional data encryption or sophisticated protection mechanisms, dark watermarks can still be identified and extracted. Once the information characteristics of a dark watermark are understood, it is possible to modify or even completely remove it, thereby undermining its original purpose of tracking and tracing. This situation not only weakens the security of digital products but also results in corresponding losses for copyright holders. Summary of the Invention

[0005] Aiming at the shortcomings of existing watermark technology in the traceability of research report PDFs, especially the problem that image watermarks are easily cleaned, resulting in the inability to effectively track and trace the source, the present invention proposes a watermark adding method. Based on this method, more accurate and efficient document protection can be achieved for PDF research reports, and convenience is provided for tracking and tracing the watermark.

[0006] In order to solve the above technical problems, the first aspect of the present invention provides a PDF research report tracking method based on dark watermark, comprising:

[0007] Get the PDF document of the original research report;

[0008] Slice the watermark information to be added, and determine the watermark information to be added to each page based on the watermark information to be added and the number of pages of the PDF document of the original research report;

[0009] Encrypting the watermark information after slicing;

[0010] Use random or pseudo-random methods to adjust the distribution of watermark information on each page of the PDF document;

[0011] Add encrypted watermarks to PDF documents based on distribution locations.

[0012] In one embodiment, the watermark information to be added is sliced, and the watermark information to be added to each page is determined according to the watermark information to be added and the number of pages of the PDF document of the original research report, including:

[0013] Divide the watermark information to be added into multiple watermark slices;

[0014] Determine the number of watermark characters to be added based on the basic information characteristics of the characters to be added and the number of pages of the PDF document of the original research report;

[0015] Determine the number of pages to be watermarked based on the character length of the watermark to be added and the number of watermark characters to be filled;

[0016] According to the relationship between the page number and the number of pages to be watermarked, the position of the watermark characters to be added to each page is determined.

[0017] In one embodiment, encrypting the watermark information after slicing includes:

[0018] Set the mapping relationship between watermark characters and mapping values;

[0019] Obtaining a mapping value of the watermark character according to the mapping relationship;

[0020] Obtaining a font size value feature according to the mapping value;

[0021] Each watermark character included in the slice is converted into a preset character with a font size corresponding to the font size value feature.

[0022] In one embodiment, the distribution position of the watermark information on each page of the PDF document is adjusted randomly or pseudo-randomly, including:

[0023] Adjust the distribution position of the encrypted watermark information on the PDF document page according to the current page number. When the current page number is odd, the encrypted watermark information is distributed in the four corners of the PDF page; when the current page number is even, the encrypted watermark information is distributed in the upper and lower edges of the PDF page.

[0024] In one embodiment, when the current page number is an odd number, the encrypted watermark information is distributed in the four corners of the PDF page, including:

[0025] Set the number of characters contained in each corner;

[0026] Determine the starting position of the characters distributed in each corner based on the size of the PDF page and the position coordinates of the lower left corner;

[0027] According to the starting position of the characters distributed in each corner and the interval between the characters, the distribution positions of all watermark characters in each corner are obtained.

[0028] In one embodiment, when the current page number is an even number, the encrypted watermark information is distributed on the upper and lower edges of the PDF page, including:

[0029] Set the number of characters contained in the upper and lower edges respectively;

[0030] Determine the starting position of the characters distributed at the upper and lower edges based on the size of the PDF page and the position coordinates of the lower left corner;

[0031] According to the starting positions of the characters distributed on the upper and lower edges and the intervals between the characters, the distribution positions of all watermark characters on the upper and lower edges are obtained.

[0032] In one embodiment, the method further includes: tracing the source of the watermarked PDF research report, specifically:

[0033] Analyze each page of the research report PDF document after adding the watermark, and determine the distribution position of the watermark characters on each page according to the page number;

[0034] Positioning the encrypted watermark information based on the distribution position;

[0035] According to the font size of the encrypted watermark character, the encrypted watermark information is decrypted to obtain the original watermark character;

[0036] The original watermark characters are summarized and sorted to obtain the originally added watermark information.

[0037] Based on the same inventive concept, the second aspect of the present invention provides a PDF research report tracking and tracing device based on dark watermark, comprising:

[0038] Original document acquisition module, used to obtain the PDF document of the original research report;

[0039] The slicing module is used to slice the watermark information to be added, and determine the watermark information to be added to each page according to the watermark information to be added and the number of pages of the PDF document of the original research report;

[0040] An encryption module is used to encrypt the watermark information after slicing;

[0041] A position adjustment module is used to adjust the distribution position of the watermark information on each page of the PDF document in a random or pseudo-random manner;

[0042] Watermark adding module, used to add encrypted watermarks to PDF documents according to distribution location

[0043] Based on the same inventive concept, the third aspect of the present invention provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, it implements the PDF research report tracking and tracing method based on dark watermarks described in the first aspect.

[0044] Based on the same inventive concept, the fourth aspect of the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and runnable on the processor. When the processor executes the program, the PDF research report tracking and tracing method based on dark watermarks described in the first aspect is implemented.

[0045] Compared with the prior art, the advantages and beneficial technical effects of the present invention are as follows:

[0046] This invention provides a PDF research report tracing method based on hidden watermarks. The method first obtains the original research report PDF document; then slices the watermark information to be added, and determines the watermark information required for each page based on the watermark information to be added and the number of pages in the original research report PDF document; then encrypts the sliced watermark information; and then adjusts the distribution of the watermark information on each page of the PDF document using a random or pseudo-random method to add the encrypted watermark to the PDF document. The method slices the watermark information itself, dividing the complete watermark information into multiple fragments and distributing these fragments across different pages of the entire PDF document. Even if some parts of the watermark information are erased, the complete watermark information can still be restored from the remaining intact parts, thereby achieving accurate tracing. Encrypting the watermark information prevents it from being easily rewritten or erased due to its intuitive nature. Even if an attacker can detect the presence of the watermark, the encryption makes its actual content difficult to decipher, greatly increasing the difficulty of tampering with the watermark information and ensuring its stability and reliability. Furthermore, a dynamic watermark position adjustment strategy is introduced. By changing the specific position of the watermark on each page of the PDF document in a random or pseudo-random manner, the difficulty of identifying and erasing the watermark is increased, and the concealment and durability of the watermark are enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0048] Figure 1 This is an overall flow chart of a PDF research report tracking and tracing method based on dark watermarks in an embodiment of the present invention;

[0049] Figure 2 This is a flow chart of slicing watermark information in an embodiment of the present invention;

[0050] Figure 3 This is a flow chart of watermark character encryption processing in an embodiment of the present invention;

[0051] Figure 4 This is a flow chart of dynamic adjustment of watermark character position in an embodiment of the present invention;

[0052] Figure 5 This is a module structure diagram of a PDF research report tracking and tracing device based on dark watermark in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] To address the shortcomings of existing watermarking technology in PDF research report traceability, particularly the issue of image watermarks being easily removed, which results in an inability to effectively trace the source, this paper proposes a novel PDF research report traceability method based on dark watermarking. This method primarily achieves more accurate and efficient document protection and traceability through the following technical means:

[0054] 1. Watermark Information Encryption Algorithm. To prevent the watermark from being easily rewritten or erased due to its intuitive recognition, this invention uses an encryption algorithm to encrypt the watermark information. This makes it difficult to decipher the actual content of the watermark even if an attacker can detect its presence. This greatly increases the difficulty of tampering with the watermark information and ensures its stability and reliability.

[0055] 2. Dynamic watermark position adjustment. A common problem with traditional watermarking technology is that watermark information is often fixed in the same position, allowing attackers to remove it through targeted cleaning operations. To address this issue, this paper introduces a dynamic watermark position adjustment strategy. By randomly or pseudo-randomly changing the specific position of the watermark on each page of the PDF document, it increases the difficulty of watermark identification and erasure, enhancing the watermark's concealment and durability.

[0056] 3. Watermark Information Slicing. In addition to adjusting the watermark's position, this invention also proposes a method for slicing the watermark itself. This involves dividing the complete watermark into multiple fragments and storing these fragments on different pages throughout the PDF document. The advantage of this approach is that even if some parts of the watermark are erased, the complete watermark can still be restored from the remaining intact parts, enabling accurate tracing and source tracking.

[0057] Through the comprehensive application of the above three technical means, the present invention effectively improves the protection level of watermark technology in PDF documents, ensuring that the integrity and availability of watermark information can be maintained even in the event of malicious attacks, providing a more secure and reliable protection barrier for the document.

[0058] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0059] Example 1

[0060] This embodiment discloses a method for tracking the source of PDF research reports based on dark watermarks. Figure 1 ,include:

[0061] S1: Get the PDF document of the original research report;

[0062] S2: Slice the watermark information to be added, and determine the watermark information to be added to each page according to the watermark information to be added and the number of pages of the PDF document of the original research report;

[0063] S3: Encrypt the watermark information after slicing;

[0064] S4: Using a random or pseudo-random method to adjust the distribution position of the watermark information on each page of the PDF document;

[0065] S5: Add an encrypted watermark to the PDF document according to the distribution location.

[0066] Specifically, S2 slices the watermark characters to be added, which means dividing the complete watermark information into multiple fragments and storing these fragments in different pages of the entire PDF document. The advantage of this approach is that even if some parts of the watermark information are erased, the complete watermark information can still be restored through other undamaged parts, thereby achieving accurate tracking and tracing. When the watermark information is a string, the individual characters are obtained after slicing. S3 encrypts the watermark information after slicing, and can use an existing encryption algorithm or a custom encryption algorithm. S4 means that the distribution position and distribution strategy of the watermark information on each page are different, and then S5 is used to add the corresponding watermark to each page of the PDF document. In the specific implementation process, the transparency of the watermark can be set to be completely transparent, thereby achieving an invisible dark watermark effect, and finally integrated into the PDF document with the watermark added (new research report PDF).

[0067] In one embodiment, the watermark information to be added is sliced, and the watermark information to be added to each page is determined according to the watermark information to be added and the number of pages of the PDF document of the original research report, including:

[0068] Divide the watermark information to be added into multiple watermark slices;

[0069] Determine the number of watermark characters to be added based on the basic information characteristics of the characters to be added and the number of pages of the PDF document of the original research report;

[0070] Determine the number of pages to be watermarked based on the character length of the watermark to be added and the number of watermark characters to be filled;

[0071] According to the relationship between the page number and the number of pages to be watermarked, the position of the watermark characters to be added to each page is determined.

[0072] Specifically, the basic information characteristics of the watermark characters include the range and type (letters, numbers), etc. Based on the basic information characteristics of the original watermark characters and the range of the research report PDF pages, a comprehensive assessment is conducted to determine the number of watermark characters required, that is, the number of characters per page. Then, based on the relationship between the length of the original watermark characters and the number of watermark characters required, the number of pages required (i.e., the number of pages to be watermarked) is determined, and finally the location of the watermark characters is determined.

[0073] Figure 2 It shows the complete process of watermark information slicing processing. represents the original watermark, Indicates the total number of pages in the PDF research report, and each page corresponds to a character , Indicates the page number.

[0074] For example, if the number of watermark characters to be filled in each page is 10, the original characters are assumed to be variables , by calculating the length of the original watermark character and dividing it by the number of padding characters per page and rounding up (i.e. function, indicating that the calculation result is rounded up), the number of PDF pages that need to be filled with the complete watermark information The calculation is as follows:

[0075]

[0076] Traverse each page of the research report PDF and determine the starting position of the characters that should be filled in the current page by the page number:

[0077]

[0078]

[0079] The slice of watermark characters filled in the current page is:

[0080]

[0081] After the watermark characters to be filled in each page are determined, the watermark characters can be encrypted.

[0082] Figure 3 It shows the encryption process of watermark characters. Represents the original watermark, i represents the index position of the character in the current watermark string rendStr, Indicates the length of the original watermark, that is, the number of watermark characters contained.

[0083] In one embodiment, encrypting the watermark information after slicing includes:

[0084] Set the mapping relationship between watermark characters and mapping values;

[0085] Obtaining a mapping value of the watermark character according to the mapping relationship;

[0086] Obtaining a font size value feature according to the mapping value;

[0087] Each watermark character included in the slice is converted into a preset character with a font size corresponding to the font size value feature.

[0088] Specifically, first, a custom mapping relationship between characters and mapping values is implemented (a set of mapping processing algorithm logic). The principle is to ensure that a bidirectional one-to-one mapping can be achieved (bidirectional one-to-one mapping, that is, the original character A can be mapped to B through the mapping logic, and the original character A can be obtained by calculating B in reverse). The mapping value range is determined. For example, the mapping value range is determined to be (0, 100). In this embodiment, the original characters are limited to characters in ASCII code, and the decimal numbers corresponding to their ASCII codes are mainly characters between 30 and 127. Therefore, the mapping relationship can be set as:

[0089]

[0090] Assume that there is a single character variable char (the character in the watermark), and get the mapped value according to the mapping algorithm logic . Then convert this value ( ) Get a new variable value through formula conversion font size value characteristics), the conversion calculation formula is: . Thus the original character The information is converted into the font size value feature of a fixed character renderChar, whose font size value is For example, suppose If the variable is the character "A", the decimal number of the character The calculated value is 41, which is calculated using the mapping formula is 11, and the final calculation is The value is 5.11, that is, the original character is finally processed into the font size feature value of a fixed character. If the fixed character If it is set to "#", the character "A" will be converted to "#" in the PDF watermark. The font size is 5.11. Similarly, the character "B" will be converted to "#" and the font size is 5.12.

[0091] In actual application, this fixed character (preset character) can be used as required. The value of can be specified arbitrarily, such as: a, 6, #, &, etc. After the watermark encryption algorithm is processed, the original watermark is converted into this fixed character Combination of multiple different font sizes, the spacing between adjacent characters is 6 (greater than or equal to 6, that is, greater than all maximum value of ).

[0092] In one embodiment, the distribution position of the watermark information on each page of the PDF document is adjusted randomly or pseudo-randomly, including:

[0093] Adjust the distribution position of the encrypted watermark information on the PDF document page according to the current page number. When the current page number is odd, the encrypted watermark information is distributed in the four corners of the PDF page; when the current page number is even, the encrypted watermark information is distributed in the upper and lower edges of the PDF page.

[0094] Specifically, the use of a random or pseudo-random method to adjust the distribution of watermark information on each page of a PDF document means that the distribution and strategy of the watermark information on each page are different, thereby increasing the difficulty of recognition. In this embodiment, the method used is to adjust the distribution of watermarks based on the parity of the pages. In other embodiments, the distribution of watermarks can be adjusted according to other methods.

[0095] In one embodiment, when the current page number is an odd number, the encrypted watermark information is distributed in the four corners of the PDF page, including:

[0096] Set the number of characters contained in each corner;

[0097] Determine the starting position of the characters distributed in each corner based on the size of the PDF page and the position coordinates of the lower left corner;

[0098] According to the starting position of the characters distributed in each corner and the interval between the characters, the distribution positions of all watermark characters in each corner are obtained.

[0099] In one embodiment, when the current page number is an even number, the encrypted watermark information is distributed on the upper and lower edges of the PDF page, including:

[0100] Set the number of characters contained in the upper and lower edges respectively;

[0101] Determine the starting position of the characters distributed at the upper and lower edges based on the size of the PDF page and the position coordinates of the lower left corner;

[0102] According to the starting positions of the characters distributed on the upper and lower edges and the intervals between the characters, the distribution positions of all watermark characters on the upper and lower edges are obtained.

[0103] Specifically, Figure 4 The dynamic position adjustment process of watermark characters is demonstrated.

[0104] Specifically, assuming that the number of watermark characters filled in each page is 10, the position of the watermark characters on each page is determined according to the dynamic adjustment algorithm and combined with the PDF page number. Here is a dynamic position algorithm logic, assuming that there are two ways to distribute the character positions:

[0105] For odd-numbered PDF pages, place the watermark in the four corners of the PDF, for example, with three characters in each of the two left corners and two characters in each of the two right corners. Assuming the width and height of a PDF page are width and height, and the coordinates of the lower left corner are (0, 0) and the upper right corner are (width, height), the starting coordinates of the four corners (lower left, lower right, upper left, and upper right) can be set to (x, y), (width - x - edge × 2, y), (x, height - y - edge), and (width - x - edge × 2, height - y - edge), respectively. x = 5 and y = 5 must be positive. The coordinates of the remaining characters in each corner are simply calculated by adding edge to the x coordinate of the previous character (because edge is the space between characters). This yields the coordinates of all watermarked characters. In practice, the dynamic adjustment range of the x and y values can be increased to achieve customization.

[0106] For even-numbered PDF pages, the watermark is placed at the top and bottom edges of the PDF, for example, with five characters on each side. The starting positions of the bottom and top edges correspond to the following coordinates: (x, y), (x, height - y - edge), where x = 20 and y = 5. In practice, you can increase the dynamic adjustment range of the x and y values to achieve customization as needed.

[0107] In one embodiment, the method further includes: tracing the source of the watermarked PDF research report, specifically:

[0108] Analyze each page of the research report PDF document after adding the watermark, and determine the distribution position of the watermark characters on each page according to the page number;

[0109] Positioning the encrypted watermark information based on the distribution position;

[0110] According to the font size of the encrypted watermark character, the encrypted watermark information is decrypted to obtain the original watermark character;

[0111] The original watermark characters are summarized and sorted to obtain the originally added watermark information.

[0112] Specifically, according to the method of adding dark watermarks mentioned above, reverse logic positioning can be achieved. When tracing the source, each page of the research report PDF document can be parsed, the position of the watermark characters on each page can be determined according to the page number, and the corresponding rendered watermark characters (encrypted watermark information) can be found at the corresponding position. According to the font size of the rendered watermark characters, combined with the watermark encryption algorithm, decryption is performed to obtain the original watermark characters. And through the watermark slicing algorithm, the original watermark information is summarized and sorted. Combined with the specific business system, the visitor information of the research report PDF resource is obtained, thereby confirming the source of the PDF resource leak.

[0113] In general, the watermarking method of this invention, which includes watermark information slicing, watermark information encryption, and a dynamic watermark position adjustment mechanism, implements a method for tracking and tracing PDF research reports using dark watermark technology. This method can efficiently and securely mark the visitor information of PDF research reports, ensuring that the dark watermark is not easily erased, thereby enabling accurate and rapid tracking and tracing in the event of a resource leak. Overall, this invention improves the efficiency and accuracy of tracking and tracing PDF research reports, providing new technical support and application examples for tracking and tracing PDF resources in the field of financial technology.

[0114] Example 2

[0115] Based on the same inventive concept, this embodiment discloses a PDF research report tracking and tracing device based on dark watermark, see Figure 5 ,include:

[0116] The original document acquisition module 101 is used to obtain the PDF document of the original research report;

[0117] The slicing module 102 is used to slice the watermark information to be added, and determine the watermark information to be added to each page according to the watermark information to be added and the number of pages of the PDF document of the original research report;

[0118] The encryption module 103 is used to encrypt the watermark information after the slice processing;

[0119] A position adjustment module 104 is used to adjust the distribution position of the watermark information on each page of the PDF document in a random or pseudo-random manner;

[0120] The watermark adding module 105 is used to add an encrypted watermark to the PDF document according to the distribution location.

[0121] Since the device described in the second embodiment of the present invention is the device used to implement the dark watermark-based PDF research report tracking and tracing method described in the first embodiment of the present invention, those skilled in the art will be able to understand the specific structure and variations of the device based on the method described in the first embodiment of the present invention, and therefore will not be described in detail here. All devices used in the method of the first embodiment of the present invention fall within the scope of protection of the present invention.

[0122] Example 3

[0123] Based on the same inventive concept, the present invention further provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the method described in the first embodiment is implemented.

[0124] Since the computer-readable storage medium described in the third embodiment of the present invention is the computer-readable storage medium used to implement the dark watermark-based PDF research report tracing method in the first embodiment of the present invention, those skilled in the art will be able to understand the specific structure and variations of the computer-readable storage medium based on the method described in the first embodiment of the present invention, and therefore will not be described in detail here. All computer-readable storage media used in the method of the first embodiment of the present invention fall within the scope of protection of the present invention.

[0125] Example 4

[0126] The present invention also provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method described in the first embodiment when executing the program.

[0127] Since the computer device described in the fourth embodiment of the present invention is the computer device used to implement the dark watermark-based PDF research report tracking and tracing method in the first embodiment of the present invention, those skilled in the art will be able to understand the specific structure and variations of the computer device based on the method described in the first embodiment of the present invention, and therefore will not be described in detail here. All computer devices used in the method of the first embodiment of the present invention fall within the scope of protection of the present invention.

[0128] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0129] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0130] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention. Thus, the present invention is intended to include such changes and modifications to the embodiments of the present invention if they fall within the scope of the claims and their equivalents.

Claims

1. A PDF research report tracing method based on dark watermark, characterized by: include: Get the PDF document of the original research report; Slice the watermark information to be added, and determine the watermark information to be added to each page based on the watermark information to be added and the number of pages of the PDF document of the original research report; Encrypting the watermark information after slicing; Use random or pseudo-random methods to adjust the distribution of watermark information on each page of the PDF document; Add encrypted watermarks to PDF documents based on distribution locations; The watermark information to be added is sliced, and the watermark information to be added to each page is determined according to the watermark information to be added and the number of pages of the PDF document of the original research report, including: Divide the watermark information to be added into multiple watermark slices; Determine the number of watermark characters to be added based on the basic information characteristics of the characters to be added and the number of pages of the PDF document of the original research report; Determine the number of pages to be watermarked based on the character length of the watermark to be added and the number of watermark characters to be filled; Determine the position of the watermark characters to be added to each page based on the relationship between the page number and the number of pages to be watermarked; The watermark information after slicing is encrypted, including: Set the mapping relationship between watermark characters and mapping values; Obtaining a mapping value of the watermark character according to the mapping relationship; Obtaining a font size value feature according to the mapping value; Each watermark character included in the slice is converted into a preset character with a font size corresponding to the font size value feature.

2. The method for tracing the source of PDF research reports based on dark watermarks as claimed in claim 1 is characterized in that: Use random or pseudo-random methods to adjust the distribution of watermark information on each page of the PDF document, including: Adjust the distribution position of the encrypted watermark information on the PDF document page according to the current page number. When the current page number is odd, the encrypted watermark information is distributed in the four corners of the PDF page; when the current page number is even, the encrypted watermark information is distributed in the upper and lower edges of the PDF page.

3. The method for tracking and tracing the source of PDF research reports based on dark watermarks as claimed in claim 2 is characterized in that: When the current page number is odd, the encrypted watermark information is distributed in the four corners of the PDF page, including: Set the number of characters contained in each corner; Determine the starting position of the characters distributed in each corner based on the size of the PDF page and the position coordinates of the lower left corner; According to the starting position of the characters distributed in each corner and the interval between the characters, the distribution positions of all watermark characters in each corner are obtained.

4. The method for tracking and tracing the source of PDF research reports based on dark watermarks as claimed in claim 2 is characterized in that: When the current page number is even, the encrypted watermark information is distributed on the upper and lower edges of the PDF page, including: Set the number of characters contained in the upper and lower edges respectively; Determine the starting position of the characters distributed at the upper and lower edges based on the size of the PDF page and the position coordinates of the lower left corner; According to the starting positions of the characters distributed on the upper and lower edges and the intervals between the characters, the distribution positions of all watermark characters on the upper and lower edges are obtained.

5. The method for tracing the source of PDF research reports based on dark watermarks as claimed in claim 1 is characterized in that: The method further includes: tracing the source of the watermarked PDF research report, specifically: Analyze each page of the research report PDF document after adding the watermark, and determine the distribution position of the watermark characters on each page according to the page number; Positioning the encrypted watermark information based on the distribution position; According to the font size of the encrypted watermark character, the encrypted watermark information is decrypted to obtain the original watermark character; The original watermark characters are summarized and sorted to obtain the originally added watermark information.

6. A PDF research report tracking and tracing device based on dark watermark, characterized in that: include: Original document acquisition module, used to obtain the PDF document of the original research report; The slicing module is used to slice the watermark information to be added, and determine the watermark information to be added to each page according to the watermark information to be added and the number of pages of the PDF document of the original research report; An encryption module is used to encrypt the watermark information after slicing; A position adjustment module is used to adjust the distribution position of the watermark information on each page of the PDF document in a random or pseudo-random manner; Watermark adding module, used to add encrypted watermarks to PDF documents according to distribution locations; The slicing module is specifically used for: Divide the watermark information to be added into multiple watermark slices; Determine the number of watermark characters to be added based on the basic information characteristics of the characters to be added and the number of pages of the PDF document of the original research report; Determine the number of pages to be watermarked based on the character length of the watermark to be added and the number of watermark characters to be filled; Determine the position of the watermark characters to be added to each page based on the relationship between the page number and the number of pages to be watermarked; The encryption module is specifically used for: Set the mapping relationship between watermark characters and mapping values; Obtaining a mapping value of the watermark character according to the mapping relationship; Obtaining a font size value feature according to the mapping value; Each watermark character included in the slice is converted into a preset character with a font size corresponding to the font size value feature.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the dark watermark-based PDF research report tracking and tracing method as described in any one of claims 1 to 5 is implemented.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the dark watermark-based PDF research report tracking and tracing method as described in any one of claims 1 to 5 is implemented.

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