"You can't edit a PDF - that bit's easy."

hmmm...I believe that you actually can. See this company, which has a number of programs to do .pdf stuff.

In this day of complex technology, I do not think there is any easy way to safeguard CDs or other text......except possibly encrypting it, and controlling the password.....and if it were going to be widely distributed, each copy would have to have its own password.

That being said, I HAVE seen programs that will create encrypted .exe files, which being clicked on, ask for a password.