If you've recently removed a door from its frame to replace it with another door that will use hinges in different locations or that will hang on the other side of the frame, or if you don't plan to fill the space with another door, you'll need to fill in the cutouts you made in the door frame when you first installed the hinges.
Things You'll Need
Cut shims to match the dimensions of the hinge cutouts.
Insert a shim into the cutout. Attach it using your hammer and a nail or two. Sand it until it sits flush with the frame or door edge.
Cover the shim and any open spaces with wood putty. Scrape the surface flat. Allow the putty to dry completely.
Sand away any excess wood putty. Paint over your work to match it to the rest of the door frame or door. Repeat with remaining hinge cutouts.
For metal doors, use metal hinge fillers and skip the putty and painting steps; just attach the fillers inside the hinge gaps with the screws included with the fillers.
Wear a mask and protective eye wear while sanding.
Paint in ventilated areas or outdoors.