VisibleThread Docs does not directly support comparing 2 excel spreadsheets. However there is a workaround that can work pretty well.
1. take sheet 1 in workbook 1, save as pdf from Excel. Call this pdf 'sheet 1.pdf'
2. take sheet 1 in workbook 2, save as pdf from Excel. Call this pdf 'sheet 2.pdf'
3. Upload 'sheet 1.pdf' & 'sheet 2.pdf' to the same folder
4. run compare against them