Often, it's more trouble than it's worth.
Just drag a copy-protected PDF over PDF Unlocker's icon, and a new, unprotected copy is created. Sure, it won't do everything that costly commercial packages do, but it can help in a quick fix in the office or at home.
Users can also strip PDF files of passwords needed to open and read them, but curiously, you need the password to do so. (Screenshot courtesy Lifehacker)