You can cut the top of the door to make it shorter, but then you will have to reposition the hinges to move the door up on the jamb. So, generally, the best way to cut the door to fit your space is to work with the bottom first. Using a table saw with a fine blade is one method of getting your outside metal door cut to size.
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Frequently Asked Questions
Can you spray paint the edge of a steel door?
Spray paint the cut edge while you have it on the saw horses. If the door has a removable sweep insert, take it out before you cut and screw it back in when done. If it doesn’t I would probably cut a piece of composite to fit, glue it and screw it then seal it up with some good silicone.