In Adobe Acrobat 7 and 8, adding a new signature when one or more other signatures have already been applied will cause Acrobat to display a warning to indicate that the document has been modified since the previous signatures were applied. In situations where multiple signatures need to be added to a document, especially if the document contains form data that must be entered by a signer, it is preferable to first certify the document to allow these changes. This document discusses how to perform certifications to prevent these warning from appearing. [Download]