Simply put, .xlsx is a file extension for the open XML spreadsheet used by Microsoft Excel from 2007 onwards. Why the change in format from earlier versions of Excel?

The converter provides read-only access to Office Open XML documents created with Office 2007. For the time being, it's Word-only and can convert those files to Rich Text Files (.rtf).

The next version of Office will fully support two new file formats, Strict Open XML and Open Document Format 1.2, Microsoft has announced. In a blog post on Monday, Office standards chief Jim ...