After installing EA 16 i faced similar issue and found that there was some issue with Registry and changing the path to EAAddins64
worked.
I think Existing EA Addins will not working as well with EA16 64bit version, as there is a change in the registry settings.
For the EA Addins,
HKEY_CURRENT_USER\SOFTWARE\Sparx Systems\EAAddins64 - 64bit Addin Registry Path
HKEY_CURRENT_USER\SOFTWARE\Sparx Systems\EAAddins - 32bit Addin Registry Path
For this MDG Office Integration,
I tried Creating a key as "EAWordImporter" and Data as "EAWordImporter.Addin" under HKEY_CURRENT_USER\SOFTWARE\Sparx Systems\EAAddins64 similar to 32bit registry entries.
This worked for me.
Thanks