How to paint a door with primer the right way. You can easily prime a door yourself. Only with these tips will the painting go much better. Step by step, I explain to the DIY enthusiast how to paint a door. Whether you're painting an exterior door or an interior door, the bottom of the door needs to be repaired and properly painted. The bottom of the door is often forgotten. You can paint a door with a brush or a roller. And with these tips, you'll succeed!