Because rearming an application is an uncommon action, some aggressive heuristics may temporarily flag it. But a genuine, signed Microsoft file will never be classified as malware. If your copy is flagged, it’s likely fake.
You mentioned "download verified." Be extremely cautious if you are downloading this file from a third-party website (not Microsoft.com). ospprearmexe download verified
The only safe way to obtain a verified copy of ospprearm.exe is to install it via Microsoft Office itself. Because rearming an application is an uncommon action,