DAT files are created by a variety of programs, ranging from video games to video editors to word processors. There are as many types of .DAT files as there are programs that are able to open them. In order to open a .DAT file on your computer, you have to know the exact program that was used to create it.
Navigate to the location on your computer that houses the .DAT file you want to open. The exact location will vary by computer and user.
Right-click the .DAT file you would like to open, and a pull-down menu will appear. Select "Open With," and a list will appear on the screen with all of the programs installed on the computer.
Search through the listing of the programs you have available to open the .DAT file with. Click the program used to create the .DAT file.
Click "OK". If the file was indeed created with the program you selected, the .DAT file will load, displaying its contents. If not, a prompt window will appear, stating that the file is not compatible with the program. If the first program you selected does not open the .DAT file, repeat the process in a similar program (such as trying out Adobe Photoshop after Adobe Illustrator fails to work). However, if the process continues to fail, your only other method is to repeat the process with every program available on the computer until the .DAT file loads.