NWD files contain the full project data - unlike NWF fileswhich only contain references to said data. This is why the NWD format can be seen as a screenshot of project files from a given moment - it can be viewed without having access to the CAD project itself.
If you cannot open the NWD file on your computer - there may be several reasons.
The first and most important reason the most common is the lack of a suitable software that supports NWD among those that are installed on your device.