Docx is a new document format that was introduced by Microsoft in Microsoft Office 2007. It replaced .Doc as the standard format of Microsoft Word Documents. Docx is based on the new standard for Office files(spreadsheets, word processing documents etc) called Office Open XML, which replaced the previous binary and 2003 XML formats.
Docx files cannot be opened in older versions of Microsoft Office without prior conversion to Doc format.
Related: What is a Xlsx...
