When looking for PDF protection software to copy protect PDF, one usually starts by typing those words into a search engine page. But today it is not so straight forward because search results are mostly populated with articles about password protection for Adobe PDF which can easily be removed and of little use when passwords can be simply shared which does not prevent unauthorized distribution at all.
Any document that can be read in a generic reader like Adobe Reader cannot be securely copy protected because the PDF needs to be encrypted and then it requires a proprietary reader, one that can decrypt the PDF when certain conditions are met, to display the PDF contents.

Also with a proprietary PDF reader one can employ digital rights management (DRM) to control who can open the PDF. Secure DRM methods utilize more than simple password protection to restrict user access by locking the PDF to the user's computer. Each computer is then identified by either their MAC (network) address or by hard drive serial number, making it impossible for other user's to open the Copy protected PDF unless their computer can be validated also.
Validation of computers for DRM access rights may require an online call to home, to a DRM server to check the author's list of approved users, or it may require the presence of an encrypted token file stored in the same folder as the PDF on the user's computer.
There is more to copy protection than just the limitation of user access because when the PDF is open on the desktop it can be saved or copied by various methods including PrintScreen and screen capture software. Not many PDF protection software cater for such protection because they cannot interact at system level where it needs to be actioned. Nor can they prevent printing when it comes to the use of printer drivers that enable a user to convert the encrypted and protected PDF back to a normal PDF or any other file type that they desire.

But how anyone ever finds good PDF protection software in the soup delivered in today's  search engine results is surprising. However, a good place to start is with CopySafe PDF Protection, the recommended choice when the protection of your intellectual property and your livelihood can be at risk.
Available for desktop reading with DRM, CopySafe PDF Protection not only provides the best protection, but it includes support for everything that you will ever need including an online book store to sell ebooks, DRM portal to manage subscribers, online book cover design tool and the most secure solution to copy protect PDF form all types of copy plus the prevention unauthorized distribution.
For those who want to publish copy protected PDF on their web pages, CopySafe PDF Protection includes plugins for Drupal, Joomla, Moodle and WordPress which anyone can use to copy protect PDF on the web site.