Of course it will stay, and that's the sad part. Copy-protection and similar measures never is in the best interest of the customer (and the positive effect they have on sales is arguable), as it will always cause more hassle (computer games that take forever to start because of your old CD drive, audio-CDs that won't play on your computer, DVDs and the regional code, etc.).
The only way to stop these trends is at the beginning. Once it's established there's hardly a way to get rid of them.
The customers will get used to the DRM, because some day it'll be the "natural thing" for PDFs. But IMHO that's not a good thing.