A doc file format would be a possibility that I wouldn't eliminate just yet. The error message would imply it is possibly recoverable. If you open it with a text editor, is there a clue as to a file format in the first few lines?

I don't know what else to suggest but perhaps if you loaded the file to a 'dropbox' or shared drive and posted a link (via private message if it sensitive) I could take a look to see if I can suggest or recover anything.

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Andrew Lockton
Chrysalis Design, Melbourne Australia