We have some software producing a spreadsheet in the Microsoft Office XML file format (introduced in Office XP) and would like to convert this to the newer OOXML format that has been used with Office 2007 and later (the zipped xml format).
Is there any software to do so? Windows-only is fine, but preferably open source and working on Linux. I do understand that Office 2007 and later is probably able to do so, but alternative free software would be the best.