You’re trying to enlarge the hole in the strike plate, right? If so, you’d use a dremel, but the proper way to do it is to move the plate. That involves filling the old screw holes and enlarging the mortise with a chisel.

Usually you shim the door hinges if you need a tighter fit. If the strike plate is too tight, use a chisel to remove the wood under the plate. Cutting the strike plate will ruin the finish. Maybe you need to move it slightly?

I want to grind out a small portion of a door's strike plate so it latches better. The metal is not very thick but I'm not making good progress with hand files. There must be some small grinder bit I can use for this with my drill. Any suggestions appreciated.