Take the door off and remove the sweep. Some brands have the actual bottom of the door recessed a bit, which would allow the bottom flange to be cut, then re-install the sweep.
A new door could be ordered cut down from the millwork distributor, it would have to be shimmed at the sill to allow clearance for the new floor and to have the head trim line up with the old. I think it was about $100 list for the cut-down. I'd check with a lumberyard rather than a box store if you opt for the latter.