Not trying to be rude but the help guides (i think its the common functionality user guide) have heaps of information on exporting review models.
There are some things in the help guides which are ambiguous but this one is pretty solid.
The file extension should be .rvm which can be imported into Navisworks. In Navisworks its a simple open model while making sure all of the extensions are available
here try this.
1. utilities--> export --> create
2. on output file: C:\TEMP\Output.rvm -->the file name is up to you..
3. set to 'binary'
4. click on the design explorer the site your want to convert and then click add ce on export diaglogue box. you can add many site as you want
5. you can set representation and rule class below button,
6. last click export.
7.after finished open the .rvm file using full vertion navisworks and save to .nwd...
my reference pdms 12.1 sp4.7