Trying to finish a basement, and where we intend to put a partition
wall with a door is right where a contractor left a 6" duct below the
floor joists. He did this to go under a piece of microlam that is
used of support in that part of the house.

I know better than to cut into the microlam, but can I purchase a some
ductwork that will flatten out in the area where it will pass under
the microlam and hug the ceiling ?
If I could recover 2" I could install a standard interior door without
modifications.

Thanks