If the DAT file is a video, you can open it with its associated video app. However, if you aren't sure what app it's intended for, VLC Media Player should be able to open it as well.

When you double-click on a file in Windows, it will automatically open a default program that is configured to manage these types of files. It is common, though, want or need to use a different ...

Via this procedure, Windows saves your latest preferences each time you make a change and lets multiple users use the same computer with their own preferences. The name NTUSER.DAT comes from Windows ...