Files with DAT extensions contain raw data that can be anything from plain text to videos. If the file size is over five megabytes, try opening it with an audio and video player, such as Windows Media Player. If the file fails to open, use Notepad to open the file.
When opening a DAT file in Notepad, a lot of gibberish appears if the file is a binary file. Look for hints about the parent program used to create this file. Alternatively, open the DAT file using a Hex editor, which displays the content in Hexadecimal form. The name of the parent program usually appears near the beginning of the content. Open the DAT file with the parent program to read it.