I began to explore the terrain for a Word plugin for the company I’m working at.

• Although there is a common format for the manifest file, Outlook and Word add-ins seem to require separate files. I haven’t seen any add-in in AppSource that serves as both a Word and an Excel add-in.

• Microsoft provides a tool called Script Lab that allows you to run arbitrary scripts and test APIs directly within Office.

• For authentication, it is recommended to open a browser window to your web app using the Dialog API.

• It is usually not possible to use iframes to obtain authentication tokens from the task pane or sidebar itself. See this answer for more details.

• It is possible to add elements to the right-click menu in Word for add-in commands.