Unlike an extension like xls, which is used almost exclusively
for Excel spreadsheets, the doc extension has a number of
different uses; different programs use it in different ways, so
there's no answer to your question. What is the dat file you want
to open, and for what purpose? Where did you get it?
Just about every program installed uses .dat files, they can be opened with
WordPad. Right click on the file and click Open With and then pick WordPad
from the list. Good luck reading it.
