Buy door paint and a a 6" foam roller and tray. Take it off the hinges and drill 2 pilot holes for #12 deck screws about 4" from each side on the top and bottom of the door. Lay out a drop cloth with 2 saw horses on it. Door on the horses then drive 4- 3" #12 screws in the pilot holes but leave 1" exposed. Use the screws to support the door and you can do one side, then with a helper, flip the door using the screws and paint the other side. Remove all the hardware b4 you start.
They painted them white so you could see the filth that needed to be cleaned.
Recent experience so the lessons are fresh.