With Digital Rights Management controls we are able to enforce our copyrights and prevent intellectual property theft of our PDF documents. Some of the capabilities which DRM provides to protect PDF documents include control over unauthorized viewing, copying and printing, and disabling print screen and screenshots. These controls can be extended to locking the PDF documents to particular computer/s so as to prevent sharing with unauthorized parties. However, these controls can only be implemented securely by means of a PDF viewer which the authorized users need to have in order to view the protected documents. The most common type of such a viewer is Adobe Acrobat, but as we all know it has been plagued by security flaws and cracks.
The most innovative way to protect PDF documents is by having a document viewer which works in two main ways. The first way is when the user seeks to access the document for the first time. Here the viewer will check to see if it has the correct code needed to decrypt the document. If not, it will check with a licensing server to see if the user has permission to access and use the document. If permissions exist the decryption code will be sent securely to the viewer, otherwise it will display a message telling the user to contact the author to obtain the relevant permissions. The second way to protect PDF documents is for subsequent document access whereby the document viewer has to check with the licensing server to see if the user is still authorized to use the document or whether it has expired.
The most advanced PDF security viewers can decrypt DRM-protected documents on-the-fly in memory. This provides the benefit that the documents are not saved to disk in decrypted format to a temporary location which can be manipulated by the user. Companies offering DRM to help protect PDF documents must therefore have their own document viewers, to ensure that all the controls which the author wants to apply over his/her PDF documents are adhered to.
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