Mark the position of the curtain rod on the door with a pencil. Do not extend the rod too far on either side of the window in the door or the curtain may interfere with the door's operation. Line up the ends of the curtain rod with the sides of the window opening in the door.
Drill pilot holes for the curtain rod hardware. Use a drill bit that corresponds to the size screw included in the hardware.
Arrange the curtain rod on the door, in the position you marked. Center the screw holes in the rod hardware over the pilot holes you drilled.
Use a wall anchor to keep the hardware from pulling out of a hollow door. Insert the anchor in the pilot hole, then insert the screw. Turn the screw with the screwdriver until the head of the screw is flush with the curtain rod hardware. Repeat for all screws.
Hang your curtain on the curtain rod. Snap the rod into the curtain rod hardware.