When I change an excel file from xls to xlsx I do as follows: open the file i PP, Save as xlsx outside PP and then Properties/New version and select the xlsx file from my desktop. When I then open the file i PP the file format is xlsx.xls. Is there another way of doing this? As far as I can see, there is no problem to use xlsx if it is used from start when you create a document by selecting a file from outside PP.