Trim any jagged edges with a sharp utility knife. Then inject some of that foam into the hole until it starts to ooze out. Let it harden.
Once it is hardened, use a putty knife or a 5-in-1 painter's tool to remove the excess foam from the door. You want the foam to sit just below the surface of the door.
Next, use a putty knife that's wider than the hole you're filling to apply some wood filler. This will ensure a nice, even patch and save your from having to do more work later on. Allow the filler to dry and then sand it even with the rest of the door.
Once the job is seamless, all you have to do is prime and paint. This job is so easy you'll wonder why you didn't do it sooner.
