Overview of tools and methods for protecting PDF documents

PDF (Portable Document Format) is a standardized format for storing and distributing text and graphic documents. Unlike other popular formats (.txt, .rtf, .doc and others), PDF has a number of important advantages.

First of all, it is a self-contained format, and it will be displayed equally on different devices. The appearance of the document does not depend on the availability of the necessary fonts or other features on the computer. This is especially important for preparing documents for subsequent printing - on paper they will look exactly the same as on the screen.

This and a number of other useful features of the format (compact size, scalability, etc.) have made the de facto standard for exchanging and storing documents of the broadest profile - books and full-color magazines, forms and reports.

The popularity of the PDF format in business poses an important requirement for it - the availability of access control technology. At the same time, protection is required for the PDF document regardless of its purpose. It can act as a product and in the form of an e-book or marketing report to be distributed among the masses of users, or wear a trademark with limited use within the company.

General approach to protection

The built-in PDF security features are fairly simple and support the following features:

However, these methods have several significant drawbacks. Firstly, the technologies used are openly described, and there are a number of programs (both paid and free) that allow you to remove restrictions from a file in just a couple of mouse clicks. The second drawback of built-in security tools is that they are not suitable for organizing DRM schemes and controlling the actual use of a PDF file.

Where standard tools fail, specialized third-party solutions come onto the scene. The approaches used in them also vary. There are three main areas for improving the protective mechanisms of the format:

        
  1. Non-standard use of available tools of the PDF format itself.

        

    Although the PDF format is primarily intended for the transmission of static text and graphic information, it also supports a number of interactive features. One of them is the execution of user scripts in the javascript language. With their help, you can organize an additional layer of file protection, and for this you will not need any third-party tools. Although this method is very elegant from a technical point of view, since it does not depend on the platform on which the document is opened, nevertheless, there are a number of limitations. In many cases, javascript support in the viewer program may be disabled for security reasons. Recently, there have been more frequent cases when javascript is used in pdf files for malicious purposes - for example, to infect a computer with viruses. Another disadvantage is the weak security of the security code itself and the limited nature of its functionality. Javascript is a high-level scripting language in which programs are plain text. Despite possible tricks to protect the code from analysis, for example, obfuscation, it is usually quite simple to understand the principle of the program and thus bypass the defense mechanisms. The functionality that can be implemented in such a language is also often very limited.

  2. Using the mechanism of "plugins" (extensions) for existing viewers.

        

    Standard Adobe PDF Reader supports extension technology - its functionality can be supplemented by external modules. Using this module, you can implement additional mechanisms for protecting PDF files. When you open a document, the plugin performs the necessary checks and implements the necessary restrictions or other functions. Although such a mechanism is already more flexible than the first method, it also has many shortcomings. First of all, the module is “tied” to a specific viewer program and the platforms on which it exists. Thus, to support different viewers, a similar plug-in will have to be developed separately for each viewer. Moreover, on a number of platforms (for example, on mobile devices), such technology is not supported at all. Although the plugin can be well protected from learning and modification, the main weak link remains - the viewer program itself. Usually it is not protected in any way, and this allows you to intercept valuable information outside the plugin.

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  4. Finally, the third way is to implement your own viewer for a PDF document with all the necessary protective mechanisms.

        

    Obviously, this is the most expensive way. But it also gives maximum control over the document and security. In some cases - for example, when used on mobile platforms, this option is the only one available. At the same time, not only the task of ensuring the security of the document lies on the shoulders of the developers, but also providing a comfortable environment for viewing and using it.

  PDF protection Plugin Protection Own viewer

Security

Low

Middle

High

Functionality

Restricted

Middle

Unlimited

Compatibility

Middle

Low

Unlimited

Implementation complexity

Middle

Middle

High

StarForce uses a third method - developing its own viewer program to provide a high degree of protection and ease of use. StarForce Protection is based on three basic components:

        
  1. Converts a file to a format that cannot be opened with standard software. Therefore, after protection, the PDF file can be uploaded to the site for free access or transmitted in any way and on any medium.

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  3. Providing an authorized reader with a serial number for activation, during which the protected PDF file is linked to a specific user device, which prevents the copying and unauthorized distribution of the protected file.

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  5. Activation control through the personal account of the service.

Currently, the viewer program is provided to the user in the same folder with the protected PDF document. However, if necessary, the user can refuse this, using the previously received version of the program to open the file. For more information, see the FAQ .

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