Hi threedfanatic, there is also some info in the FAQ:

https://moi3d.com/faq#Q:_Why_can_I_export_to_.obj_format.2C_but_cannot_read_.obj_format_into_MoI.3F

Usually .obj files contain polygon mesh data which is a different kind of model data than the CAD solids and surfaces that MoI is designed to work with.

- MIchael