The Serializer.pkg in this gist is signature by Microsoft Corporation Official.
Here is the official download link for Microsoft_Office_License_Removal tool. If you alaways been asked for 'Sign in' and still requires activation, please try to remove Office license files on a Mac. Run Microsoft_Office_2019_VL_Serializer and it will automatic activate Office 2019 Manual download and install Microsoft_Office_2019_VL_Serializer.pkg
