XLS files are Excel workbook files created in Excel 97 or Excel 2003. The 2007, 2010 and 2013 versions of the program use the XLSX format by default to save workbooks, but can also use the XLS format.
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Don't just hit save: 5 Excel formats that will change the way you work
Upgrade from standard Excel workbooks to specialized formats that shrink, shield, and streamline your spreadsheets.
Spreadsheets that contain complicated formulas and a lot of data can take a while to load when you open them in Excel 2007, but that's not the only reason spreadsheets can be slow to load. Microsoft ...
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