How's being quite without moving the money stealing? If somebody owns that money, and does have a backup as well, taking it and hiding it somewhere in your place gives him the opportunity to figure out he lost the paper wallet, and that he must move the funds as soon as possible.
The act itself is not stealing. The intention of what you are going to do later might be. If you want to do the right thing or try to do the right thing, why would you keep quiet about it? The owner maybe only has that one copy. If you remained quiet, how would they ever know that someone found it?
Think of something else instead of a bitcoin paper wallet.
I find a watch on the beach. I take it home with me, put it in my drawer, and decide not to do anything about it. I might not wear the watch, I haven't sold it or exchanged it for something else, but I took possession of it and it's currently in my control.