Visual Studio For Office Runtime -

Implementing the IDTExtensibility2 interface, which allows Office and your custom code to "talk" to each other. Why You Need It

The Visual Studio for Office (VSTO) runtime is a software component that enables the execution of VSTO add-ins in Microsoft Office applications. VSTO is a development tool that allows developers to create custom Office add-ins using .NET programming languages such as C# and Visual Basic .NET. visual studio for office runtime