Video Tutorial - Add a new button on Office backstage using C#

How to add a new button to Office (Excel) Backstage from Addin using VSTO (C#)

The following XML adds a new button on Backstage. The button will be added at the end as we didn't specify a location.

What is a Backstage view and How to customize it?

Backstage view in Office 2010 - An Introduction

Backstage was introducted in Office 2010 to hold commands and menus which are do some work 'on the document', for example, Printing, Publishing to SharePoint etc.

Backstage view is part of Office Fluent UI and very much customizable. The following video shows the elements of Backstage view.

Office 2010 BackStage View - An Introduction to customizable elements