I still have the installer file and the product key for it. I am currently migrating to a different computer with the same operating system 10.12.6.
Totally commiserate! (Funny how so few people actually read the OP.) I'm trying to use the SAME Mac with the SAME OS, (new SSD) and I cannot. I've even tried loading an older version of Office and moving the files you mentioned. There has to be another file somewhere that contains a link to the code embedded in the 3 files.
The Microsoft activation servers are indeed offline *for 2011,* though they'll let you enter your activation code, all ~30 digits, before vaguely telling you that they couldn't verify it. They could indicate that certain versions' codes are no longer going to be provided before we waste 20 minutes entering codes that worked even as recently as a month ago. The phone activation service IS still available. How much money can they be saving by refusing those of us who CANNOT upgrade due to OS requirements, other old software licenses, etc.
Certainly puts me off this subscription-service push. I don't need a new copy of Word, nor do my clients. Since we no longer have access to standalone product key options to support the computers we've been using for the last 10 years—if we're to follow big tech's recommendations—there would soon be many more machines in a landfill that otherwise are perfectly functional. Intuit, of all companies, still gives activation codes for QuickBooks at least as far back as 2013! Wow, Intuit beats Microsoft in support... Never thought I'd see the day!
There's always LibreOffice, and OpenOffice. We're investigating these options, because an El Cap Mac cannot run Office 2016, which is also now deprecated in favor of 2019.
I'm thinking about collectors, historians, and forensic analysts needing old hardware. Up to about 2011 — the point where commercial software started to be obtained/activated from app stores and the cloud — hardware could still be curated. After that, a great deal of major software requires some kind of IPv6 activation. In a few years, if you need to open a file created on hardware from 2015? Sorry, no software can be found or activated for any hardware in that year, including the OS.