| b0uncer |
05-06-2010 01:46 PM |
I doubt if it's possible, because if it's intended to be read at all, one must be able to decrypt and access it, and if the information is available for reading, it is available for printing. The only way I see is that the document can be opened only by using say Adobe Reader, which decrypts an encrypted document on the fly, doing some heavy work to protect the data from being read while it's in the memory, and prevents printing from that program completely. Even then you could take screenshots and print them, losing quality but effectively being able to print the contents piece by piece. Since other programs can read pdf files, even encrypted ones, than just Adobe Reader and because even encryption is not safe, it is quite impossible to have a waterproof method. You can restrict distributing only to persons you trust (of course using encryption, signing and such usual methods) and try to legally forbid them from redistributing or printing the document, but if somebody wants to print the thing, that somebody can and probably will. In the end it's a matter of trust more than anything else; if you don't trust anybody, you may not give the document to them. One of the safest methods would be to control the physical presentation device as well (paper or screen), and show it to the reader(s) from there but not letting them get their hands on it themselves. Though again somebody might have a camera hidden somewhere, which allows saving the document as digital pictures and printing them later, after some image editing. Paranoid, but possible.
The same applies to other formats than pdf just as well.
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