If it's superficial, wood putty or bondo, then sand/prime/paint.
If it's into the hollow area, stuff with paper towels then seal up with expandable foam insulation. Then scrape even and you are ready for putty and go forward.
If the door slit open like mine did we put a piece of wood the length of the door under inside the bottom of the door and screwed it in then painted the bottom and the screws so not to see it
What is the problem with the door?
If the wood is chipped, gouged or missing you could use a technique like this: https://www.hometalk.com/diy/repair/furniture/repairing-wood-damage-with-bondo-41583831
Repairing Wood Damage With Bondo
Please describe the problem with the door. Is this a closet door? A picture would help.
If it's superficial, wood putty or bondo, then sand/prime/paint.
If it's into the hollow area, stuff with paper towels then seal up with expandable foam insulation. Then scrape even and you are ready for putty and go forward.
If the door slit open like mine did we put a piece of wood the length of the door under inside the bottom of the door and screwed it in then painted the bottom and the screws so not to see it