Can your doors be fitted into my existing door frame?

Usually yes, if the frame is sound, square and the correct depth. Measure the existing leaf — width, height and thickness — and send us photos of the hinge mortises and latch strike. If the frame is out of square by more than a few millimetres, or the jamb depth is unusual, a new frame or a pre-hung unit will give a far better result than forcing a new leaf into an old frame.