Docx is a new document format used that was introduced by Microsoft in Office 2007 and later versions for Microsoft Word documents. Docx follows the new standard for documents from Microsoft called Office Open XML which is also known as OOXML or OpenXML.

People using older versions of Microsoft Office, prior to Office 2007 cannot directly open Docx files, however you can find some tools and converters for converting docx files to a different document format that you can view on older Office versions.