To open a DAT file, double-click on it, and select the first option in the dialog box that lets Windows automatically detect the default application with which to open the file. If that doesn’t work, use the program that generated the DAT file to open it.
In case the DAT file is a video file with the .dat extension and you don’t have the necessary program installed, download and install VCDGear or CyberLink PowerDirector. After opening the file, save it in a more common video format to convert it and allow other similar programs to run it. If the DAT file is part of an email attachment, upload it to an online conversion service such as Winmaildat.com, and download the content from the results page once the service extracts it.
If the DAT file contains only textual content, open the file by double-clicking on it, clicking on the second option in the dialog box and selecting a text processor utility such as Notepad or WordPad. In case you’re certain that a DAT file you received via email is a Microsoft Word document or an image file with the .dat extension, you can change it to the appropriate format by clicking on the file, pressing F2 and changing the .dat extension to .doc or .docx in case the file is a Microsoft Word document, or .jpeg if it’s an image file.