I manually created a DOCX document, attached to an email, and then sent it to my wife in hopes it would fail when she attempted to open it. Alas, her converter (installed via the MS AutoUpdate) worked as designed.
Perhaps her success is a consequence of the original document being created on my Mac and the DOCX being manually appended. The MS default for file extensions is lower case and cannot be changed on my machine, or I would have tried that.
The sooner I can break her machine, the sooner she gets mine, and I get a new one.