Docx is the new file extension standard for ms word 2007 documents, you can load the documents into MS Word 2007 and then “save as” office 97-2003 document.
However there are times that we might encounter files from colleagues or clients in the DocX format. Unfortunately, MS Word 2003 cannot open these files. After some googling… I found that Microsoft themselves have come up with a Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats which you can readily download and install yourselves.
Upon installing this compatibility pack. You can already open any .docx and .docm formats saved document in MS Word 2003 (minus some of the features found in MS Word 2007 of course).
For the download page click here Source :http://www.windowsreference.com/ms-office/how-to-convert-documents-with-docx-to-doc/