title: Using VBA, open an OpenXML format (.docx) document in Word 2003 where the extension is not .docx or .docm
body: <p>I have a Word add-in that writes and reads Word documents in OpenXML format - i.e. .docx.</p>
  
  <p>But so that I can easily recognize "my" documents as against normal Word .docx files I have used another extension, call it .myx (or .mym for macro-enabled documents).</p>
  
  <p>This all works wonderfully in Word 2007 and Word 2010, and I thought it would work in Word 2003 (with the Compatibility Pack installed).</p>
  
  <p>But Word 2003, while it opens documents with .docx extension, will not open a .myx document, unless I rename it so that the extension is .docx.</p>
  
  <p>When I try it with VBA, I have used a number of what look like obvious values for the WdOpenFormat enumeration, but nothing seems to help.</p>
  
  <p>Do I really have to change my extension to .docx to get Word 2003 to open it? </p>