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 ...

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.