It would appear that most of the corporate world is still running Office 2003, which is fine - I am sure you have your reasons! But why the F*(K haven't you deployed the compatibility pack to view Office 2007 documents?
The hassle more than likely comes back to the sender (you!!) with a request to change the format of their documents, and although it isn't really my problem I have to oblige (otherwise, they may not pay my invoice).
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RANT OVER
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The script below will convert any Office 2007 (DOCX) files in a folder to a Office 97-2003 (DOC) format using the Office automation API.
get-childItem
-filter *.docx | foreach {
$doc = "$($_.fullname)"
$2000doc = $($doc.substring(0,$($doc.length - 1)))
$office = New-Object -ComObject word.application
write-host "Opening - $doc"
$word = $office.Documents.Open($doc)
write-host "Saving - $2000doc"
$word.SaveAs2000($2000doc)
$word.close()
$office.quit()
}