Do I need a wood hardener for worn door hinge screw holes?
You want to fill the hole in with solid wood. Wood hardener will harden the wood, but still not provide anything for the screw to bite into. Wood fillers won't have enough grip to hold a door...

There are several easy ways to do this. If you have some scrap wood around, you can cut a chunk out that is a bit bigger than the screw hole, cover it in wood glue and hammer it into the hole. Or you can buy a piece of dowel from the hardware store. Just be sure it's a big bigger than the hole, and use glue. Don't worry if the plugs sticks up a bit at first. When the glue is dry, trim the plug with a chisel. If you don't have a chisel, you can use a utility knife to trim the plug down to the surface.