Lay the door on two sawhorses, positioning the sawhorses near the ends of the door so the door sits stable. Measure and mark the portion of the side of the door that needs to be cut off, using a carpenter’s square to make a straight line.
Cut along the line you drew, using a utility knife, providing a channel for the saw blade to cut through. This helps minimize any splintering from the door’s wood along the cut line.
Lay a 2-by-4, that is as long or longer than the door, parallel to the line. Position the board so the saw’s guide will touch the edge of the board, and the saw blade lines up perfect with the line. Clamp the board to the door at both the top and bottom.
Cut the door along the line, using a circular saw. Sand along the edge of the door where you cut, using fine-grit sandpaper, until the edge is smooth.