Hi, .tlb-files cannot be added to your project via an #include. One way is to use Qt's dumpcpp utility, for example: C:\Qt\5.15.2\msvc2019\bin\dumpcpp C:\Program Files\ASCON\KOMPAS-3D v20\Bin\kAPI5.tlb" then with a bit of luck you'll have 2 new files: kAPI5.h and kAPI5.cpp, Add these files to your project. And then try #include the kAPI5.h file in your main.cpp.