Using VSTO to Share Documents

I'm not sure that I want to do this, but while doing a bit of research, I can't seem to get an answer. I know that MS Word documents can be shared, and opened for collaboration, co-editing, conversations, and so forth. This is pretty easy to do already, but there is a chance that I'd like to automate who gets the document shared with them, and I'm not sure that's possible, or just possible on Office 365, or I'm missing something. No search I have tried has come up with much of anything at all. Not for, not against, just nothing relevant. That can always be just me.

I've seen that MS Graph allows for a fair amount of automating collaboration, but that appears to be Office 365, which I don't have access to now, but will have at some uncertain time in the future. Some folks are saying that it will be in the near future, which they've been saying for a couple years, by now. Until that time, I have Office....uh, whatever the latest that isn't 365 is.

So, what I'm asking is whether or not VSTO add-ins can get at the sharing mechanism in an MS Word document and automate it? After that, I'll figure out whether or not I care.