I upgraded to Office 365 64-bit version after uninstalling the 32-bit version on my desktop. After installation, the Outlook Mail Options "Signatures" and "Stationery and Fonts" will not open. I'm running Windows 10 Pro.
I am not an expert in regards to this. But I did some research and was able to find an article that should help you out here. Hopefully that will help get you in the right direction. In the meantime, maybe another member with prior experience to this subject could offer more insight.