Power cuts, system and software failures can cause Autodesk Navisworks to close before you can save changes to your file.
Autodesk Navisworks can automatically save backup versions of a file you are working on, enabling you to recover your work if Autodesk Navisworks closes abnormally.
Auto-saved files have an .nwf extension, and named as <FileName>.AutoSave<x> where <FileName> is the name of the current Autodesk Navisworks file, and <x> is a number that increments with each auto-save. So, for example, if you work with a file called Enviro-Dome.nwd, the first auto-saved file is called Enviro-Dome.Autosave0.nwf, the second auto-saved file is called Enviro-Dome.Autosave1.nwf and so on.
You can control a number of Auto-Save options, such as how often Autodesk Navisworks saves your work, the location of backup files, and the maximum number of backup files you want to keep.