title: Saving an OpenXML Document (Word) generated from a template
body: <p>I have a bit of code that will open a Word 2007 (docx) document and update the appropriate CustomXmlPart (thus updating the Content Controls in the document itself as they are mapped to the CustomXmlPart) but can't work out how to save this as a new file.! Surely it can't be that hard!</p>
  
  <p>My current thinking is that I need to open the template and copy the content into a new, blank document - file by file, updating the CustomXmlPart when I encounter it.
  Call me old fashioned but that sounds a little bit clunky to me!</p>
  
  <p>Why can't I just do a WordprocessingDocument.SaveAs(filename); ...?</p>
  
  <p>Please tell me I am missing something simple here.</p>
  
  <p>Thanks in advance</p>