Forgive me I am a little behind the times. I am now trying to figure DRMs out. I understand what it is suppose to be, but what I want to know is how is it implimented in pdfs?

Adobe's DRM system requires you to register with them as a company - I'm afraid I don't know the details although I believe it's non-trivial. However, I suspect by far the best and easiest way would be simply to go through DriveThru RPGs and let them deal with the details.

In terms of implementation, the .pdf has some data in it that Adobe's readers look at and refuse to let you read without the proper authorisation. Authorising stores a bit of data on your computer saying you can read this .pdf. It's horrible insecure and serves mostly to merely irritate legitimate customers.