A family of Microsoft word processing software products for creating web, email, and print documents.
One more thing to be aware of: When you use Save As in a *.doc and tell it to save as a *.docx or *.docm, there's a check box in the Save As dialog for "Maintain compatibility with previous versions of Word". To enable "Mark comment done" and other Word 2013 new features in that document, you must be sure that box is not checked.
The other way to do this is to click File > Convert and then save.