Microsoft .NET uses a system called COM Interop to bridge this gap. The Autodesk.Inventor.Interop.dll acts as a wrapper. It translates .NET commands into native COM commands that Inventor understands, and vice versa.
Lesson 3: A First Look at Code for my First Inventor Plug-In autodesk.inventor.interop.dll
If you need to find the file manually, you can locate it in your Inventor installation folder: C:\Program Files\Autodesk\Inventor [Your Version]\Bin\Public Assemblies\Autodesk.Inventor.Interop.dll . Microsoft