Docx is a new file format for files created in newer version of Microsoft Office software. In case you are using old version of MS Office software and you receive docx word file created in newer version of MS Office, you cannot open that file in existing Office on the Mac computer.
XML Covnverter Add-on for Old MS Office
You can add feature to open docx files in your old MS Office software by installing Open XML File Format Converter for Mac 1.0.2. Click here to downloadÂ this addon. When on the webpage, scroll down and see he download links at bottom-right part of the webpage.
Online Docx to Doc converter services
Use Safari to open Docx files on Mac
You can use Safari to open Docx files on your Mac computer. Change Docx extension to Zip and then unzip the file. Open Safariand goto file > Open Now, Navigateto /insert_name_of_Word_file_here/word/document.xml and read the text of docx file. source