When you reach a door/window frame, allow the paper to hang over the door or window while you smooth the paper until it meets the door/window frame. Once the area is smoothed, cut off the paper that hangs over the door/window, leaving only a few inches for trimming. You will want to make a diagonal cut in the paper at the corner of the door/window frame, allowing the paper to lay flat at the edge of the frame. Smooth the paper down around the corner. Use your putty knife and a sharp blade to trim the excess paper around the door/window frame.