That may be difficult on older painted doors.
Plane hinge side of door.
Complete one pass per stroke with a hand or power planer with.
On many doors the grain runs from top to bottom instead of side to side.
Immobilize it with a doorstop and plane it in place see step 3.
Hold a belt sander plane or power plane at about a 45 degree angle to the edge of the door and remove material to the witness line.
Before trying to trim the door open it and examine the hinges.
Test each screw by tightening it with a screwdriver.
A hinge can often work loose binding the door against the frame.
People usually try to plane off the edge.
Running the plane in this direction will create smooth cuts instead of chunky bumpy cuts.
But frequently the solution is on the hinge side.
Plane the hinge or lock sides of the door in the same direction as the wood grain applying light pressure to remove very small amounts of wood at a time.
Step 2 use your ruler to measure 1 8 inch from the jamb to the start and end points on the door.
But for maximum control and to plane longer portions take the door off its hinges with a screwdriver or drill.
The radius of the mortise is determined.
Use a pencil to mark this area on the side of the door not on the edge.