This is a VSTO plugin because the new Office API does not have access to footnotes
Go into the project properties and generate a certificate under the Signing tab.
"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin\msbuild" <path/to/sln/file> /target:publish /p:SignManifests=true /p:ManifestCertificateThumbprint=<thumbprint/from/certificate> /p:Configuration=Release;PublishDir=<publish/directory> /p:SignAssembly=true /p:AssemblyOriginatorKeyFile=<path/to/certificate/file>
Note: Your path to MSBuild may vary
For distribution you will need a Code Signing certificate from a place like Digicert