Open the bypass doors on the door frame. Grasp one door in both hands and lift slightly to raise the rollers on the doors from the track. Pull the door toward you to remove it from the track. Take the other door down in the same way.
Remove the screws holding the track in place on the top of the door frame, using the screwdriver or drill. Hold the track up against the door frame with one hand while removing the last screw. Take down the track from the doorway.
Fill the screw holes left behind in the door frame, using wood filler. Spread the filler over the holes with a putty knife and allow the filler to dry for at least 45 minutes Sand the filled holes with sandpaper until the holes feel even with the rest of the door frame.
Drive wood screws into the hinges on the inside edge of the door. Place one hinge 4 to 5 inches down from the top, one hinge 4 to 5 inches from the bottom and one hinge roughly in the middle of the door.
Hold the door up to the door frame so the top of the door sits roughly ¼ inch below the top of the frame. Push the hinges out so they sit against the door frame. Mark the screw holes for the hinges in pencil.
Drive a screw into the top screw hole of the top hinge. Once the screw is in place, move to the bottom of the door and drive a screw through the bottom hole of the bottom hinge so it lines up with the mark made for that screw.
Secure the door by driving screws through each of the remaining screw holes in the door. Open and close the door to make sure it sits properly in the doorway, tightening screws as necessary.