Doors are commonly made with fiberglass because it's lightweight and durable. Another good characteristic of fiberglass is that it will not dent like metal will. Fiberglass is also softer than metal, and is fairly easy to drill or cut. A common way to decorate doors, or just to cover the window, is to hang curtains on the door. Mounting curtains on a fiberglass door is easy and can be done by anyone who can use a drill.
Determine where on the door you want to mount the curtain rod, and hold it in place. Center the curtain rod by measuring from the end of the curtain rod to the edge of the door on both sides. When the measurement is the same on both ends, the rod is centered.
Level the rod out by measuring from the top of the door to the top of the rod on opposite ends. When the measurements are the same, the rod is level with the door. Keep holding the rod in place.
Mark the location of the screw holes onto the door with a sharpie marker. Take the rod down and put it to the side.
Drill the holes using an electric drill with a drill bit that is 1/16 inch smaller than the mounting screws. Wrap the drill bit with masking tape so only 1 inch of the tip is showing. This will be a guide so the drill bit doesn't go through both sides of the door.
Hold the rod in place over the drill holes, and insert the screws into the holes. Tighten them down using a screwdriver.