Measure the hinge edge of your door 5 inches down from the top, and 10 inches up from the bottom. Mark these measurements with a pencil. If you have an existing door jamb with hinges, hold your new door up to the opening and mark where the hinges meet the door.
Hold the top hinge on the edge of the door at the upper pencil mark. Trace around this hinge with a pencil. Repeat this process with the bottom hinge and mark.
Cut around the hinge tracings with a sharp utility knife. The cuts should be as deep as the hinge is thick.
Use a sharp wood chisel and begin removing the wood inside the tracings, where the hinges will be sitting. Hold the chisel at a low angle to the door. Work slowly to avoid unnecessary mistakes.
Continue carving until both hinge locations are entirely carved out. Once done, the hinges should be able to sit flatly in the spaces and be flush with the edge of the door.