If the DAT file you're trying to open is text, you can convert the file into text in the Microsoft Excel program by first saving it as a CSV file.

How to Automatically Convert an Excel File to Text Using Visual Basic. Microsoft's ubiquitous spreadsheet application, Excel, is a useful tool for small and large businesses alike.

A CSV file is a simple text file that you can open in a wide variety of programs, including any program that works with plain text like the Notepad app.

Luckily, Excel offers handy formulas that allow you to convert text into upper case, lower case, title case, and even sentence case with minimal effort.