A DAT file is a generic data file. It contains data that may be opened or referenced by a specific application. While some DAT files can be opened directly, most contain program data that is referenced the program when it is running. Therefore, most DAT files are not meant to be opened manually.

Since ".dat" is a generic extension, it may be used by multiple programs. This can make it difficult to know how to open a DAT file. However, if the DAT file is saved in a text format, you can view the contents of the file by opening it in a text editor.

A DAT file may also be a video file from a Video CD, or VCD disc. DAT files are typically found in the \MPEGAV\ directory of VCD disks and contain MPEG video data. They can be opened directly by supporting video playback programs.

Files named Winmail.dat contain formatting information for Rich Text (.RTF) messages sent from a Microsoft Exchange Server. A Winmail.dat file may be appended to the end of an e-mail when the recipient's e-mail client does not support RTF-formatted messages.