On my site, which focuses on the hobby of collecting celebrity autographs, I offer a PDF file of celebrity address listings. I use Acrobat PDF password security to deny printing of this list. I realize the weaknesses inherent in this and that this could be easily hacked. In fact, a visitor to my site recently sent me an email asking for "an un-encrypted, un-password protected file" which would save him the time, effortm and the $20 that he would have to spend on a program that could easily break through the password. Is there any other reliable means of PDF security that could not be broken with a $20 program?
Whatever you use the end user can copy the list. Does it have to be a pdf? You could generate the pdf from a php script on the fly with authentication before the pdf is sent to the user but they can still copy it and send it to their friends. Why not give users unlimited lifetime updates of the information (like seobook does) that way anybody with a pirated copy will have out of date details.