Unmanaged API reference (Office development in Visual Studio)
Applies to: 
Visual Studio 
Visual Studio for Mac
Note
This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here
Starting with the 2007 Microsoft Office system, Office applications use the IManagedAddin interface interface to call into a VSTO Add-in loader component that is included with the Visual Studio Tools for Office runtime. This component is used to help load-managed VSTO Add-ins. You can create your own VSTO Add-in loader component by implementing this interface.
Note
Interested in developing solutions that extend the Office experience across multiple platforms? Check out the new Office Add-ins model. Office Add-ins have a small footprint compared to VSTO Add-ins and solutions, and you can build them by using almost any web programming technology, such as HTML5, JavaScript, CSS3, and XML.
In this section
A COM interface that you can implement to load and unload managed VSTO Add-ins in Office applications.