Without the inclusion of Section breaks, the page layout cannot change as a result of a copy/paste operation. Period.

What may change is the paragraph formatting, but that is an entirely different matter and can be affected by whether you're using Styles properly and/or what copy/paste settings you have Word configured for. These are user issues, not a Word problem, per se, and there is no Word setting you can use to prevent it.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]