If you are sure that the .dat file is PDF and want to open it as a PDF, right-click on the .dat file and select Open with. Then, you will see the list of programs to open with.

Though DAT files, which house data as the shortened name implies, are usually best left alone, here's how you can open them.

If you're having trouble opening a DAT file, I'll show you a simple and free way to do it. This method works on both Mac and PC. Just open your browser and go to winmaildat.com. It's a ...