I don't know from Mail Merge—I've done it a few times, but not often enough to remember how—but it seems all you want, at least for now, is to copy a document with a known path and name to a new document with the current path and a calculated name. Nothing hard or complex about that, right? What am I missing?

First you calculate the new Word document name, probably using this formula:
Then you have code that fetches a copy of the template (so to speak) from the old location, and copy it to C:\<current path>\<calculated filename>.

Either I've misunderstood you, or there's some part of that you don't know how to do. If the latter, which part? I don't want to insult you by telling you all the things you already know and leaving out the one part that's confusing you.

For the copying part, you could open up the Word application, then do an Open and a Save-As. But I'm sure it'll be simpler to access some Windows feature that does file copies. Is that the part you're having trouble with? Because if it is, I'd have to google it myself. Won't be hard, though.