My old man has a bunch of .dox stuff saved. He has complicated large files saved that are not supported by any of the FOSS conversion tools. I’ve tried Libre office, Abi Word, and every command line tool and converter I can find. These are entire book sized files.
I have a W10 machine with Word. Is extracting the .exe and running it with wine feasible without making an epic mess or massive project of this?
This is what I would recommend as well. Try to convert within Word to an older version or open version that’s likely to be compatible with other software. Test one and see if it converts okay.