If the document is an email attachment, all you're doing is saving the temporary copy your email app creates when you open the file. All your edits will be lost as soon as you exit the email app. Such edits as are saved till then are written to a temporary folder; re-opening the temporary file, rather than the attachment, will give you access to those edits until you exit your email app.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]