Hi Sherri,
O.k. that helps, I will try to take what R. Scott wrote a few steps further. If the door is indeed some form of "particulate materials," it is best left to the interior of a structure. How you tell will also assess your skill sets. Take a "block plane," and plane some wood off the ends, sides, and a little off the face of a rail or panel. If solid wood is revealed great, if not, the door will only last a few seasons at best in most cases. Especially with a modern paint applied to them.
Now on finishes, I won't say "don't paint" but I will stress that most "modern paints" do little more than trap moisture inside wood and/or the material they are applied to. I typically use natural oils and if I want color, I will pigment the oil which can create an opaque stain or actual oil paint depending on formulation. You can also use a "Milk" or "lime paint" which will last a few seasons. The senescence of these natural
milk and lime finishes reveals a gradual, and pleasing effect over time. With all of these natural finishes, the key element is the protection of the underlying material they are applied to, thereby acting as a true "sacrificial layer" without inhibiting permeability, like modern latexes and other contemporary paints, which traps interstitial moisture and facilitates decomposition and deterioration.
Regards,
j