I have an Office Word add-in that I wish to make it work with Office Word 2016 for Mac. I tried looking into official Microsoft documentation and could not find anything. I want to reuse as much code as possible while still having the extension to work with older versions of Word as well as Office Word 2016.
Is there any way to do this? Any help, even if it is something remotely related to this is appreciated.
TL;DR; There is no way to do that.
Microsoft has bet on a new technology suite also called Office add-ins but web based. They are compatible with Mac. The old COM based approach (on which VSTO .NET add-in are built on) are legacy.
There is no way to reuse .NET code with this new technology, except of course to port business logic to the web server (which serves the web based add-in).
More reading on the comparison with the two add-ins generation: see this article I wrote