CAD tip # 12644:

Just test your models (documents) for a presence of the iProperty “Preprocessor“ (STEP and IGES) or “Translation Standard“ (IGES). Warning: for STEP assemblies, this property is set only in the IAM file, not in the components.

So you can e.g. use the following iLogic code with the inquiry:

Dim PV
Try 
 PV = iProperties.Value("Custom", "Preprocessor")
Catch
End Try
If PV>"" Then MsgBox("IMPORTED")

Examples of imported models: