What is the difference between Office Automation, VSTO, and Open XML SDK?

Question

What is the difference between Office Automation, VSTO, and Open XML SDK? Do we need all of them or some of them are obsolete?

Answer 1

Office Automation refers to the manipulation of an Office program (or, more commonly, an Office document via an Office program) programmatically, using COM interop.

Visual Studio Tools for Office (VSTO) is a set of development tools available in the form of a Visual Studio add-in (project templates) and a runtime that allows Microsoft Office 2003 and later versions of Office applications to host the .NET Framework Common Language Runtime (CLR) to expose their functionality via the .NET type system. As a result, it allows extensions to the Office applications to be written in .NET languages.

The Open XML SDK is a set of type classes, built on top of the System.IO.Packaging API, that can be used to manipulate Office documents conforming to the Open XML standard. Unlike COM interop, it does not require Microsoft Office.