A family of Microsoft word processing software products for creating web, email, and print documents.
At the moment, either getting or setting (say) ActiveDocument.ReadOnlyRecommended in VBA also causes an error (Named Argument Not Found).
(Also, trying to set Me.ReadOnlyRecommend to true in a module in "ThisDocument" does not work and the property is not listed in the Properties Windows for the document in the VB Editor).
Since Word 2016 still pops up the appropriate dialog box when you try to open a readonlyrecommended document, I'm going to guess that this is actually an error in the API (it sounds as if a named parameter is expected), because when you open a read only file via the user interface you still get the appropriate messages. But I really do not know. I have reported this via the smiley mechanism.
I can't see an obvious mechanism to set the value using VBA and the object model on an open document. I tried inserting an empty ReadonlyRecommended document but that did not work.
So I reckon the only way at the moment would be to insert/modify the relevant XML element in the document's XML, so the following value appears in the settings part
How to achieve that in your scenario is a different matter - if you were saving as .xml it probably would not be too hard to open the .xml file as a text file, search for the element and insert it if absent, etc., but working with a .docx would be harder, probably significantly.