I want to fit a plain flush plywood door to a downstairs toilet. The door frame is a standard width - 760mm - but the height of the frame is only 1890mm, as the floor level has been raised. The shortest door I can find in that width is 1981mm, so I need to take about 90mm off the height. Can this be done without damaging the door?
Those kind of doors are hollow core, an egg box kind of structure inside, not a problem to cut it down, just re-glue the batons back in once you've cut them off. Bare in mind the door will have a lock side, where there's a block mid way up to fix your latch and handle to, depending on where you plan to put your handle, if you take the whole lot off the bottom, you may end up missing the lock block.
get down to a decent timber yard or builders and get a 'door blank'. Its a big plywood and block timber sandwich, from which many doors are made.