Autodesk Inventor is built largely on Microsoft's Component Object Model (COM) technology. The .NET framework, which is commonly used for modern customization (C#, VB.NET), cannot directly "talk" to COM components.
that require custom User Interfaces (UI) or integration with other enterprise databases and software. For detailed technical guidance, you can explore the Autodesk Inventor API Developer's Guide or download the official Creating Add-Ins for Inventor Are you looking to build a standalone EXE internal Add-in for your project? Creating Add-Ins for Inventor - Autodesk
For a typical installation of Autodesk Inventor, the file is located in the "Public Assemblies" folder within the Inventor installation directory. autodesk.inventor.interop.dll
Reproduce the error
If you have multiple versions of Autodesk Inventor installed on the same computer (e.g., Inventor 2024 and Inventor 2026), the Windows registry might become confused about which COM object to serve. Autodesk Inventor is built largely on Microsoft's Component
You can often use a DLL from an older version (e.g., 2018) to maintain compatibility with newer versions of Inventor.
Alternatively, Inventor also installs this DLL into the Global Assembly Cache (GAC), which can be found at: For detailed technical guidance, you can explore the
With the release of Inventor 2025 and the shift towards .NET 8, the landscape for Inventor development is evolving. The SDK tools have been migrated to .NET 8, but developers have noted issues where the reference path for autodesk.inventor.interop.dll pointed to an incorrect OEM location. As Autodesk continues to modernize its platform, developers will need to upgrade their projects to .NET 8 using tools like the ".NET Upgrade Assistant" in Visual Studio 2022 (version 17.8+). While the interop assembly remains the primary gateway to the Inventor API, the surrounding development environment is moving forward, and developers must keep pace.