Doors and Windows - Short Ceiling, How do I trim down 80" doors

I am refinishing my basement. One area where I need to put a door is only 80" ceiling, but I have a 4" casing around the door jamb. All the doors at HD seem to be 80 tall standard. I don't really want to rip the casing as it will look odd as compared to other doors in the house.

I'm guessing that I want to cut off some of the bottom of the "hollow type pre hung" interior door? The doors have 4 raised rectangular patterns that start about 12" from the bottom of the door. ... you know the typical pre hung "home depot" doors.

Is the correct way to shorten the door by cuting from the bottom? I think I will need to whack about 4".

Thanks, NEJ

NEJ: Welcome. Once you determine the amount of clearance needed at the top, take the door out of the frame, and cut the case legs to that length. Mark the door bottom allowing another 1/2" if using carpet, or 1/4" if not. Using a razor knife, trace the mark with a straight edge and cut the door with a sharp circular saw. The razor cut will prevent splintering and chipping. Make sure the blade is always on the lower side of the razor line, so any chipping will be limited to the waste. Take the waste and break out the bottom plug and clean it as good as you can with a scraper. Apply glue to the 4 edges and reinsert it into the void of the bottom of the door and clamp it using a 1x on each side and clamps (plural). When dry, remove the 1x's sand the area, paint, hang, and enjoy. POst back if we can help further.