How To Convert Online Xlsx To Xls Format?

There are many online converters available which can convert a xlsx file to an xls file. Most commonly used is https://www.zamzar.com/convert/xlsx-to-xls/.
I don’t think you need an online converter for that. The XLSX format (*.xlsx) used by Microsoft Office Excel is the default file format used in Office Excel 2007 and higher. The XLS format (*.xls), on the other hand, is the default file format used in Office Excel 2003 and earlier. Office Excel 2007 is the version that followed Office Excel 2003.
Office Excel 2007 still supports worksheets created by earlier versions. That’s why you can still open and save worksheets in the 2003 format. This is the easiest way to convert XLSX files into XLS format. Open your XLSX file in Microsoft Office Excel 2007 and then click on the Office button then select “Save As.”
In the “Save as type” dropdown list, select “Word 97-2003 Document” and then click “Save.” This will then save the XLSX file into XLS format. You can now open this file in Microsoft Office Excel 2003.