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?

By default, you can't open a PDF file in Excel 2010, the spreadsheet software from Microsoft. To be able to import your data into Excel, you must export the PDF as an XML file using Adobe Acrobat ...

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 ...

Microsoft is trumpeting support for its Office Open XML document file format as an international standard from more than 300 companies and organizations on a new "community" Web site set up by the ...

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).