A fairly common problem for 64-bit Windows users is that Outlook's Stationery and Fonts or Signatures buttons won't work.
When the Stationery and Fonts or the Signatures button is grayed out or won't do anything when you click it, you may need to edit the registry.
First, empty your Temporary Internet Files. This may or may not help much, but even if it doesn't do any good, your Internet cache will be clean.
Empty your temp internet files and if it still fails, change both (Default) and LocalServer32 values in each of the following keys to the appropriate path for your installation of Outlook.
Default installation paths for Office / Outlook are:
Outlook 2010: C:\Program Files (x86)\Microsoft Office\Office14\Outlook.exe
Outlook 2013 ProPlus: C:\Program Files (x86)\Microsoft Office\Office15\Outlook.exe
Outlook 2013 Home Premium: C:\Program Files\Microsoft Office 15\root\office15
Don't forget to restart Outlook after editing the registry.
Do it for me
If you are using the default installation location for Office 2010 or Office 2013 ProPlus, you can use the registry file for your version:
To open the registry editor, press Windows key + R to open the Run command. Type regedit into the Run field and press OK to open the registry editor.