Dear Employer,
We would like to help you with your Office Add-ins.
Office Add-ins utilize the Office's Add-ins platform via XML manifest that has necessary configuration ,interface and permission info. The rest is done as a regular web page. The VSTO version had a different paradigm (COM based) and therefore was done as a components in server's echosystem.
We have done different applications/components/ Microsoft extensions before, including for SSIS and Data Factory, for example, and for the Outlook as well.
We will be happy to provide you with references.
Sincerely,
Virginia