Microsoft’s newest versions of MS Office suite now support a new file format, which for Word documents uses the suffix docx, but sadly this format is no longer compatible with older versions of Word that used the doc suffix, a binary format that in most cases could only be read by Microsoft supplied software such as Word 2003 and older, or the free Word viewer available from the Microsoft website.
For compatibility purposes, converting a docx document to doc format is sometimes a requirement, either due to other parties not having access to the MS Office suite of software, or for backup and archival purposes, although increasingly major corporations and government departments are looking to update older documents to docx format.
Docx and doc are not in any way compatible, doc being a closed binary format that cannot be read unless the correct application such as MS Word or a filter for third party applications is installed. Docx by contrast is an open standard that can be unzipped using the built-in Windows unzip utility and the document.xml file extracted.
The process of converting from one format to the other essentially involves extracting the text, any embedded objects, and the style formatting, and then re-saving these in the other format. Users of MS Office 2007 are able to select the “save as” option in the file menu of Word 2007 and select Word 97/2000/XP as the preferred format.
Users of older versions of Word such as Word 2003 or Word 2000 will need to add the Microsoft supplied compatibility pack that enhances these versions and allows full open and save in docx format, thus allowing Word 2003 and Word 2000 users to convert a docx file to doc format easily.
Whilst docx has many advantages over doc formatted documents, it is generally less supported, with many of the more popular alternatives to Ms Office only now offering full or limited support. Although OpenOffice 3.0 and new versions of Abiword promise full support, WordPerfect support for docx is still imperfect, and only allows users to open files.
Converting a docx file to doc format if MS Office isn’t available is sometimes best accomplished using an online docx converter, specialist websites that upload the original docx file to their server, perform a conversion, and then make the new doc formatted file available to download. Care should be taken that confidential or secret documents are never uploaded to third party websites making this service less useful in the corporate or government sector.
More secure converters that can be installed directly on the user’s computer are available to purchase thru major software retailers, or can be downloaded under a shareware type license that may give a free trial period. Better software allows conversion both ways and even into other popular file formats such as HTML or PDF.
Mac users can download free universal binaries that sit in the dashboard and convert docx to doc on the fly, although the preferred method suggested by Microsoft is to install Office 2008 for Mac, however several users have reported compatibility problems.
source : http://www.docx.net/how-to-convert-docx-to-doc