A family of Microsoft word processing software products for creating web, email, and print documents.
This is probably not anything related to margins at all. Open the Page Setup dialog (click either the Margins button or the Size button on the Layout ribbon and click the item at the bottom of the dropdown), and click the Layout tab at the top of the dialog.
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In the middle of the dialog, make sure the Vertical Alignment dropdown is set to Top, and not to Center or any of the other values.