Override this method to expose an object in your add-in to other Microsoft Office solutions. This includes other add-ins and document-level customizations running in the same application process, VBA code, and external automation code.
The object that you return must be public, it must be visible to COM, and it must expose the IDispatch interface. If the object you return does not meet these requirements, the Visual Studio Tools for Office runtime will throw an InvalidCastException after it calls your implementation.
For more information, see Calling Code in Application-Level Add-ins from Other Office Solutions.