PDFKey Pro is an application that lets you password-protect your PDF files. It can also be used to unlock certain files that have password protection that prevents you from copying or printing files. The app has a very minimalistic interface that looks well and works like a charm. You can drag files onto it to process them easily.
In my testing, I used Mac OS X's built-in PDF encryption tool to password-protect a sample PDF file so that it couldn't be printed or copied. Then, I proceeded to try to unlock the file with PDFKey Pro. The app said that unlocking was successful and when I opened the file, I was able to print it and copy anything in it just fine. I wasn't asked for a password or anything like that. It should be noted that PDFKey Pro can't be used to unlock PDF files that ask you for a password when you try to open them. For that, you need to know the password, or this tool won't work.
Locking files with this tool works just as well as unlocking them. You can either lock a file with a password so that it can't be opened, or so that you can't copy or print it. Both features work well. There are even different encryption algorithms that you can choose from.