How do I stop my painted wooden back door from swelling from rain?

I'd use a level and check to see if your door is plumb and square, then check the framing for the same thing. You can always chalk the side of the door, then close it to see where it sticks, then sand it down. Best of luck.

You need a new door, obviously the one you have has been comprommised in some way. Check for leaks to make sure the same thing does not happen to your new door.

You cannot not prevent wood from being wood. But you can take a plane and shave off a little bit of the wood so it doesn't stick. You can also try shooting a 3" drywall screw into the center hole of the hinges on the frame. Sometimes this helps because of the length of the screw goes past the point of swelling into the door jam.

I have the same problem with my front door. I took the electric sander and sanded the edge of the door where it was sticking....not a lot, but down to the bare wood. Now rub a bar of soap on it and see if it's sticking. If it is, just sand some more. If not, wipe the soap off and finish the raw edge with paint or poly so water doesn't get into the wood. I sanded mine two years ago and now all I have to do is use the soap if it sticks again. Piece of cake!

Paint it with an oil based paint.

Sam, do you live in a zone 5? And is it up north or towards southern part of zone. Remember that things should contract in the winter and that if you doshave off be careful as to how much since you don't want to create another problem.