FreeFlow Core wll use MS Office to convert said documents to PDF.
There are a few things that are needed:
Supported MS Office installed in the same server as FFCore
FFCore should be configured to run under a service account (details on install guides found here. Check the Optional Installation Procedures)
I would also log into the server (or connect via Remote Desktop Connection) using the service account and launch each of the MS Office applications to ensure there are no prompts that are holding up the conversion
Is there a local Xerox person that you can call upon?