Depends on what created these files. "dat" is probably the most over-used of
all file extensions -- there are literally hundreds of applications that
have used it, including (if my memory serves) some of the very early
pre-Windows versions of Word.
As a start, experiment with the options listed under 'Files of type" on
Word's File > Open dialog. Some dat files are just plain text, equivalent to
..txt. If all else fails, try "Retrieve text from any file" to recover the
content.
You'll get better suggestions if you can suggest what app created them.
