how to shorten an exterior door

As a reminder to some of the folks, there are 2.54 centimeters per inch. So there are 25.4 millimeters per inch. So it's easy enough to figure that 75 millimeters would be 3 inches, with the remaining 15 mm another 3/5 of an inch.

Actually, 3-35/64"

JeldWen has a very good customer service group. Call them and get the correct answer. They will likely suggest taking less off the bottom of the door and some off the top. That would make the modification less awkward looking.

Joe

If it's a solid-core door, you can pretty much cut off as much as you want with not problem.

If it's a hollow-core door, you'll probably cut off the whole solid piece that reinforces the bottom edge, leaving skins and insulation. You can then peel the skins off the solid piece, then glue it inside the new bottom.

Being solid core doors, I don't see a problem with removing several inches from either end without losing any integrity. In fact, the shorter the door, the more stable it will become.