Strip the Old Paint
The door in this project had latex paint applied over oil paint. It's often very difficult to sand latex paint, especially when it's applied over oil paint. Without removing this paint, the repairs we made to the door could not be sanded smooth. This meant that the paint would need to be removed using paint-stripper. An added benefit from stripping the paint is revealing the design details of the door hidden by many layers of paint.
Remove the door from the opening, place it on saw horses and lay down drop cloths. This is a job best done outdoors. If you work inside, be sure that there is adequate ventilation.
Apply the paint stripper as directed by the instructions on the container (Image 1). Let it set as long as specified in the directions.
Scrape off the paint with a wide putty knife to remove most of the softened paint. Finish removing the paint with a quality paint scraper tool (Image 2). Wide scrapers work well on flat surfaces. Pointed and shaped scrapers work well for corners and details.
Repeat the process until nearly all of the paint is gone and the wood exposed.
Neutralize the paint stripper with an appropriate liquid product as directed on the stripper instructions.
Sand the door as needed. For a door to be finished as natural wood, completely remove every bit of paint and sand thoroughly. For a door to be repainted, sand rough spots until the door is smooth and ready for paint.