User FAQs

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1) What is a COM add-in ?
This Is a type of add-in that can be used to provide additional application-level functionality
A COM add-in implements the IDTExtensibility2 interface
It has been possible to create these since Visual Studio 2002.

2) What is a VSTO add-in ?
This is a type of add-in that can be used to provide additional application-level functionality
A VSTO add-in implements the IStartup interface (which is implemented in the Addins class/interface)
This interface is strongly typed and does not rely on late binding.
It has only been possible to create these since Visual Studio 2005.

3) What is a COM Shim ?
When you build an Office Add-in, you should ensure that your code is isolated from other add-ins.
The standard way to do this is to use a COM Shim which is an ActiveX dll written in C++ that will create a dedicated AppDomain for your .NET based add-in.
If you use the built-in VSTO projects that come with Visual Studio then a COM Shim is automatically provided by the VSTO loader.