VSTO Add-ins or Microsoft Office Add-ins: Key Differences to Know
VSTO add-ins and Microsoft Office Add-ins extend the same Office apps in opposite ways. This guide compares architecture, deployment, security, performance limits and Office.js feature depth, explains why the new Outlook and the Exchange Web Services retirement put a deadline on Outlook VSTO add-ins, and sets out when to keep VSTO, when to switch and how to migrate.