i don't seem to be able to turn off the automatic conversion, but i can get around it by opening up the version history instead of launching the file directly. that did actually fix it.

it's typical microsoft, though. i point out that their service actually works, when google's and adobe's both don't, and they promptly break it by trying to force a proprietary format that i don't want on to me. fuck.

i'm actually going to delete the account and start again and hope it undoes the unwanted forced conversions.