You can use the Notepad program on your Windows 7 computer to create DAT files, but you cannot open an Excel file in Notepad without first saving it as a CSV file. The CSV format is a plain-text document type that separates values with commas, which allows you to preserve some of the Excel formatting while still being able to view the file in plain-text editors. Your converted DAT file will then prove accessible in the program that requires that format.
Double click to open your Microsoft Excel 2010 file.
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Click the "File" tab in the upper-left corner, then select "Save As."
Click the drop-down menu to the right of "Save As Type" and select "CSV (Comma Delimited)."
Click the "Save" button, click "OK" to save the active sheet, then click "Yes" to keep the worksheet in CSV format.
Right click the CSV file you just created, click "Open With" and select "Notepad."
Click "File" at the top of the window, then click "Save As."
Click the drop-down menu to the right of "Save As Type" and choose "All Files."
Click inside the "File Name" field and add ".dat" to the end. For example, if your filename is "xxxxxx," modify it so it reads, "xxxxxx.dat."
Click the "Save" button.