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Get started programming VSTO Add-ins


VSTO relies on the .NET Framework. COM add-ins can also be written with the .NET Framework. Office Add-ins cannot be created with .NET Core and .NET 5+, the latest versions of .NET. This is because .NET Core/.NET 5+ cannot work together with .NET Framework in the same process and may lead to add-in load failures. You can continue to use .NET Framework to write VSTO and COM add-ins for Office. Microsoft will not be updating VSTO or the COM add-in platform to use .NET Core or .NET 5+. You can take advantage of .NET Core and .NET 5+, including ASP.NET Core, to create the server side of Office Web Add-ins.

You can use VSTO Add-ins to automate Microsoft Office applications, extend features of the application, and customize the user interface (UI) of the application. For information about how VSTO Add-ins compare to other types of Office solutions you can create by using Visual Studio, see Office solutions development overview (VSTO).

Applies to: The information in this topic applies to VSTO Add-in projects. For more information, see Features available by Office application and project type.

Create VSTO Add-in projects

Create VSTO Add-in projects by using one of the VSTO Add-in project templates in the New Project dialog box. These templates include required assembly references and project files. Visual Studio provides VSTO Add-in project templates for most applications in Office.

For more information about how to create a VSTO Add-in project, see How to: Create Office projects in Visual Studio. For more information about the project templates, see Office project templates overview.

Develop VSTO Add-in projects

When you create a VSTO Add-in project, Visual Studio automatically creates a ThisAddIn.vb (in Visual Basic) or ThisAddIn.cs (in C#) code file. This file contains the ThisAddIn class, which provides the foundation for your VSTO Add-in. You can use members of this class to run code when the VSTO Add-in is loaded or unloaded, to access the object model of the host application, and to extend features of the application. For more information, see Program VSTO Add-Ins.

Automate applications by using the Object models

The object models of Microsoft Office applications expose many types that you can program against in a VSTO Add-in. You can use these types to automate the application. For example, you can programmatically create and send an e-mail message in Outlook, or you can open a document and add content in Word. For more information about how to access the object model of the host application in code, see Program VSTO Add-Ins.

For more information about the object models of specific Microsoft Office applications, see the following topics:

Customize the user interface of applications

There are several different ways to customize the UI of the host application by using a VSTO Add-in: