This is the wrong thing to do 1st. As he pulls the shim the door drops & he catches it holding the knob & then opens the door. Maybe he didn't carry the door & the hinge hold it, maybe not. Would need to see the whole door to tell if he's just lifting the door by the knob. The place to start with a sagging door is check the top hinge for looseness. Tighten the screws & maybe the door lifts up & free of the binding. If the screw is still loose then plug the hole with a splinter & tighten up the screw. If that doesn't work I go for a longer screw to get a better grip. I have up to 6" drywall screws to be able to find sound wood. 99% of doors fix this way. I've encountered doors with the framing behind the jamb split & unable to take a screw & removed the casing & glued (or epoxied) the frame tight again. I was taught that a door with a loose hinge will drop soon after I plane & rehang it leaving a door with a weird angled bottom when It does get repaired correctly.