This project is not for your everyday door dinger from bumping another car or object in the street --these dents require repairs that involve more than a hammer and body-filler. We're talking about a dent --one that is big enough to stretch the metal well beyond its original shape. For this sort of door damage, you have two options --find another door at a wrecking yard, or reskin the door you already have. Recent developments in structural adhesives make the second choice a good alternative, with no welding required.
Most sheetmetal doors are made in three pieces. There's the frame (which the inner door panel and armrest attach to), the window channel (which is welded to the doorframe) and the skin (which attaches to the doorframe and the outside of the window channel).