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.

You can also search for conversion tools based on the file extension — the three characters after the period in the file name. Example: “free PDF file converter.” ...

How to Convert an Office Data File to PST. Microsoft Outlook stores data in a Personal Folders, or PST, file; the file contains messages, contacts, notes and other information found in your Folder ...