I just went through the same problem, and here is what I found:

Two versions of Skype for Business 2016 available. The “standard” version (what is normally installed) breaks the DLLs for any version of Office other than 365 (as best I can tell); second version is “stand-alone,” which, apparently, isolates the DLLs and allows other (older) versions of Office to function properly along-side of Skype for Business.

One relevant link from Microsoft is https://support.microsoft.com/en-us/help/3139711/how-to-install-the-skype-for-business-basic-stand-alone-client

One minor caveat which I have not completely worked out: I am now getting regular errors from MS Office, saying that there is an issue and asking whether I want to “repair” my installation. Of course, I did this the first (one or two) times the error appeared. Now, I have taken to ignoring the error and, thus far, there seems to be no impact.

I will try to remember to update this thread, if I confirm this is something related to the Skype for Business installation.

Tom B)