If the door sags from weight or age, here’s an easy, fast repair.
Close the door to check the sag by looking for uneven gaps along the top and latch side. Often the top hinge side has loosened, or the weight of the door has pulled the hinge or jamb slightly away from the stud.
Replace at least 2 screws from the top hinge with longer 2 ½ to 3 inch deck of dry wall screws. Drive them through the hinge and jamb, and into the wall stud.
Check door swing to confirm the sag is gone.