You can cut it, only if the bottom of the door is solid. Typically exterior doors are solid for 1-2″ all the way around.. You could try tapping on the bottom edge to see where it sounds hollow As for cutting it, i would use a circular saw with a high toothed blade.Click to see full answer. In this manner, can u cut a fiberglass door?If it needs to be cut down to size then you can do this by using a normal saw to cut through the fiberglass door. Cutting through fiberglass is actually very simple and easy, however you must be careful that you don’t breathe in the glass fibers. Fiberglass is very easy to cut with a jigsaw. what do you use to cut fiberglass? Fiberglass panels can be cut with either a table saw or hand-held circular saw. A table saw tends to be a specialty power tool owned by series craftsmen or woodworkers with a dedicated workshop. A circular saw can be used in whatever space you plan to accomplish your construction work. Likewise, people ask, how much can you trim a fiberglass door? Some fiberglass doors can’t be trimmed at all. Others can be trimmed only along the top and bottom. Even doors that can be planed on all four sides usually can’t be trimmed by more than half an inch on each edge. It can crack.Can you cut a mail slot in a fiberglass door?Measure the area you want to cut on your fiberglass door. If you’re installing a mail slot, dog door or glass light panel, measure those items first, then transfer the measurements to your door. Draw the outline of the cut with a permanent marker and a straight edge.