Re: Opening document files
"Docx has no restrictions on content types."
Yes it does. DOCX cannot contain macros, DOCM can contain macros.
You also can't save it as a DOCM and then rename to a DOCX manually as it will no longer open due to a mismatched MIME type.
You could save it as a DOCM then rename to something else like RTF which may work, however I don't see how you can put a Macro into a DOCX unless there is a security advisory that has shown a workaround.