I'm sorry, but you are not going to get an answer here without posting the template.
How to attach a screenshot or file in this forum.

Even with the template, it may be a stretch. If you can see this property in Quick Parts > Document Property, you have a much modified Word. As far as I know, there are 15 properties that can be listed there and Document Type is not one of them.
00 deleteme 2.png

The screenshot is from Word 2010 but the list of properties is the same in 2016.

Your question is the equivalent of calling a mechanic and saying I have a customized 2017 Ford Explorer with this doohicky on it. It was part of the customization. How do I take it off? I suspect that the mechanic would either say "Bring it in so I can look at it." or "Take it back to the people who put it on and get them to help." There is no way they could tell you how to take it off.

By the way, why do you want it off? In what way is it causing you problems? Document properties describe a document. They do not change how it prints or works.