Back to the basics:
An NWC file is a cache file, only used by navisworks Simulate or Manage.
NWF is the normal format used by Simulate and Manage to review 3D models
NWD is the export that is created by Simualte and Manage that can be opened with Freedom.
Some "vertical" applications on top of AutoCAD, like Revit, have "object Enablers" to create an NWC for Simulate.
So in order to understand your question, Which CAD application are ypu using ?
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