Autodesk Navisworks has three native file formats: NWD, NWF, and NWC.
An NWD file contains all model geometry together with Autodesk Navisworks-specific data, such as review markups. You can think of an NWD file as a snapshot of the current state of the model.
NWD files are very small, as they compress the CAD data by up to 80% of the original size.
An NWF file contains links to the original native files (as listed on the Selection Tree) together with Autodesk Navisworks-specific data, such as review markups. No model geometry is saved with this file format; this makes an NWF considerably smaller in size than an NWD.
By default, when you open or append any native CAD or laser scan files in Autodesk Navisworks, a cache file is created in the same directory and with the same name as the original file, but with an .nwc file extension.
NWC files are smaller than the original files, and speed up your access to commonly used files. When you next open file or append file in Autodesk Navisworks, the data is read from the corresponding cache file if it is newer than the original file. If the cache file is older, which means the original file has changed, Autodesk Navisworks converts the updated file, and creates a new cache file for it.