The Best Way to Cut Off a Door Bottom. If you've just installed carpeting, your doors will probably rub and bind, which means that you have to trim off the bottoms.
When you need to cut the bottom of a door, use a straightedge, The skill set to hang a door included, trimming and beveling the door.
They reckon about 5mm needs to be cut off. Mark a pencil line along the bottom of the door with a block of wood 20mm thick, with the door.