If your original document has been properly constructed with Styles instead of direct formatting, you could delete all the content, then save the blank document as a Word template. Having done that, you could attach the newly-received documents to that template, via Developer|Document Template>Templates>Attach, and check the 'Automatically update document styles' property. Provided those newly-received documents have used the same set of Styles correctly, their formatting should update to conform to the attached template. No copying/pasting required.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]