The best paint 
to use on metal doors is high adhesion metal paint, usually oil-based, with a primer.
Surface Preparation
Before you paint the door, it’s important to remove any dirt, grease, and rust. This can be done by using a wire brush or sandpaper to gently scrub away the surface of your door. If you have an old paint job on your metal door that has been damaged by water or other elements, then also remove this from its surface as well.
Once all of this is done, it’s time for primer!
Paint Removal and Rust Treatment
Rust and paint removal is a simple process. You can use a wire brush to remove rust, dirt, grime, and debris from the surface of your metal door. You can also use it to remove any remaining paint that is still clinging to the metal door by brushing off any loose dust or dirt particles.
If you want to get rid of all traces of these substances while leaving behind an even surface there are other methods available such as sanding down your metal door but this may take some time depending on how bad it has been damaged in the first place so if you’re looking for something quick then using this method might not be ideal for you.
Primer
Primer is a special type of paint that prevents rust and corrosion. It’s used to cover surfaces that have been previously painted or to make them easier to paint. Primer can also be used in combination with other paints on metal surfaces (like primer + oil-based enamel) for added protection against rusting.
Primer might seem like an odd choice for your door, but it actually makes sense if you consider what you’ll be doing next: cleaning it! The cleaner the surface gets when primed, the easier it will be for us to clean up any gunk from previous owners’ parties or accidents—and we’ll save time by not having to sand down each spot several times before painting over them again later on down the road!
Paint your metal door
Paint is the only thing that will protect your metal door from rust, weather, and the elements. This is why you should always use paint to finish off your project; it’s the final coat of protection for all of those surfaces.
The best paint to use on metal doors
The best paint to use on metal doors is high adhesion metal paint, usually oil-based, with a primer.
The best primer for your door is an oil-based product that coats the entire surface of the door. Oil-based primers are more resistant to moisture than water-based primers and will help protect against rust, corrosion, and discoloration over time. A good rule of thumb: if you want to keep your door looking new for years or decades (or even centuries), choose an oil-based primer instead of water-based one.
Primer can be applied in two ways: by brush or sprayer; either way works well but both require some patience! Spray cans tend not to coat evenly so I recommend using brushes unless you’re working with large panels or plan on doing lots of touchups later on after painting.
Conclusion
Metal doors can be a great choice for any home. They’re durable, they look good and they work well as an entryway or a storefront on your property. The most important thing is to choose the right paint for your door!