A family of Microsoft word processing software products for creating web, email, and print documents.
There seem to be no syntax errors on the largest component files in the .docx. (I checked only the files that could store 3110 characters or more.) Online converters, as well as the old MS XML converter, fail as well.
However, OpenOffice did open the file, but it lost the equation forms (leaving some strings behind). And TextEdit also opens it, but does not interpret tracked changes or equations at all.
Thus, if no one else provides a better solution, try converting it with OpenOffice, then Save As .doc or .rtf, reopen in Word, fix the file and Save As into the original format. Keep copies of versions and stay away from tracked changes, choosing instead to compare versions of the file whenever you need to see the differences.