In a corporate environment, especially, you should not change the content of documents after they have been sent to external parties, or even to others within the same organization; doing so may have adverse legal consequences down the track. The only documents you should consider modifying are those created as user manuals and the like, to reflect their current status, whilst archiving the older versions with the original content.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]