After you have removed the outer handles, use a grinding wheel, or disk with a heavy grit, to deeply scratch the surface. Some newer cars have plastic or fiberglass composite outer skins (like this Fourth-Gen). Grinding deep scratches into the door will make the fiberglass and filler bond properly to the door skin. This is also important to do even when the door is made of sheetmetal.
Carefully cut the fiberglass sheeting to fit the door handle holes. Don't mix the resin up until you are ready to apply as it will harden quickly.
It's a really good idea to wear gloves at this point for obvious reasons. The fiberglass will stay wet just long enough to move into position. Notice the resin will drip all the way down the door unless precautions are taken, like paper and tape. You do not want the resin sticking to anything.
A nice big grinder will take the high spots down quickly. You won't need to sand the fiberglass completely smooth, just enough to knock the rough stuff down.
At this point it is time to smooth out and straighten up. Kitty Hair is perfect for fiberglass work because it's basically plastic filler with fiberglass hairs mixed in. It works great on sheetmetal too.
Always sand on a 45-degree angle. Enough said!
After the rough sanding is complete, feather the edges and knock down the deep sand scratches. A good filler primer will fill the scratches, and when properly blocked, leave you with a perfectly smooth finish ready for paint.
If your door has trim, like this one, it will make a perfect line to mask from, saving you from repainting the entire door. Presto-change-o, it's like they were never there. Not bad for a kid, huh?