Without seeing the actual document, one can only guess. From your additional details, it seems you may be using formfields or content controls - perhaps even ActiveX controls.

If you can attach a document to a post with some representative data (delete anything sensitive), somewhere here should be able to decipher its content pretty quickly. You do that via the paperclip symbol on the 'Go Advanced' tab at the bottom of this screen.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]