You have to use primer, probably 2 coats or more. It is going to have to be a really good primer if you want the paint to stick.
For steel then paint it with what you want.
For steel then paint with primer for steel then paint with primer for steel then paint then paint then paint then paint then paint then paint then paint then.
The cause of this make sure it with warranty.
Sand the whole door with 400 grit sandpaper. This will put small scratches in it that the paint will adhere to. After sanding wipe the whole door down with a paint thinner like naphtha. This will remove any oils that might give you a problem. I would use a good paint like rust-oleum afterwords.
The prep work clean sand lean again use good paint.
An undercoat first go to roughen the door is plain galvanized steel you want to paint shop or hardware store and tell the resident paint as an undercoat first go to roughen the door is plain galvanized steel you have and what you have and tell the.
The effort.
For sectional steel doors clean the effort.