This isn't a biggie . . . . unless you have a bedroom or bathroom door that bugs the peewadden out of you because it won't stay open. These interior passage doors in a home are usually left open and are supposed to stay that way most of the time. However every once in a while you get one that slowly but surely closes itself. You walk up to find them some semblance of the condition as in the lead photo. The fix is super simple and anyone can do it.
Step 1: Fixing Problem Doors
The underlying problem is the door jamb is not perfectly vertical. If it is vertical or even leans back from the door opening, the door will stay open. However if the jamb leans inward just a fraction of a degree, the door 'falls' into the opening. To fix this all you need to do is straighten the hinge axis back to vertical. You definitely don't want to reset the jamb but you don't need to. Just take out the jamb screws (not the door screws) in the bottom hinge as in photo 1. If it is a two-hinge door, wedge something under the door (a towel works) to keep it from falling away from the jamb. If it is a 3 hinge door, it will stay in place with no wedge.
Now take a birthday card (everyone has drawers full of those!) and cut some shims the shape of the door jamb hinge opening. Usually only two thicknesses of card will do the trick as shown in photo 2. These have already been in place so the screw holes are there, you don't need to pre-punch the holes. Photo 3 shows them in place. Now replace the hinge and screws and test the door. If it is a 3 hinge door, put one thickness of card in the middle hinge. I have found only one door that I couldn't fix with a card thickness of the hinge plate!