Hi, You need to go into the options and change the Facetting factor, this is the setting that changes how rounded an object is.
In Navisworks go to Options > File Readers > DWG/DXF/SAT > and change Facetting factor to 4. This is the recommended level that rounds objects off but doesn't degrade perfomance too much. Higher than this won't make a big difference visually but will make your machine work much harder.
If this is an exported file you can access Navisworks Options inside Plant 3D by typing NWOPT in the command line.
Lee Mullin Product Support Specialist Global Services Autodesk Ltd.