[msp_yc]

Not sure why this is downvoted, it’s absolutely correct. I tried this myself; it would have -greatly- simplified scraping Word docs because the custom tags would have been available for XPath querying. Alas, Word strips it all on open.

[blackboxlogic]

Yep, we had a similar use-case. I remember the error message pointed to a help page which pointed to an article about this patent.