The fact is that most Windows APIs are poorly documented when they are documented so AFAIK, it's conjecture but I'd say it's educated conjecture. The fact that Office changes Windows system files shows me that there are some internal Windows things that are added and/or changed by Office, an external product that doesn't need to have it's internals documented for programmers. Anyway, if the APIs are hidden, how would we know? Most of us don't work at MS.