All fonts in EngageOne Designer are being fetched from Windows Fonts directory (Default path "C:\Windows\Fonts"). Alternatively, it can be accessed via 'Control Panel' > 'Fonts' as well.
To install a new font, copy the required font file(s) and 'paste' it is in the 'Fonts'. This will install the copy/pasted fonts in the system. The EngageOne designer fetches the newly installed font and same can be used in any publication. Ensure to relaunch the EngageOne Designer after font installation.
UPDATED: August 30, 2019