What's the best way to add doc,docx support for a certain subsite?

I have a client that wants to upload Word Docs. I saw where I can "whitelist" if in wp-admin>settings and I see a few outdated plugins. I've not tried either because I wanted to seek good advice before running down either road.

I would prefer to isolate this ability on a per domain basis, but its not the end of the world to allow it globally...

As always... thanks...