Field "Duplicate Across Pages" not working

This thinking is exactly what's wrong with this software. It's so bloated and poorly ad hoc'd that it runs slower than enterprise 3D software. Quite the accomplishment. Yet Adobe knows no one will go elsewhere. Ripe for antitrust reaming. 

What Berndt Alheit  meant is that one digital signature certifies the validity of the entire document.

This is true if you're working with an agreement. But not all PDFs are agreements that can be certified with one digital signature.

Some PDFs are composed of many other forms inside the same PDF which  may require that the approving signature be applied to other many parts of the same document.

I work with government forms and the workflow suggested by Bernd Alheit doesn't adapt to my PDFs because of  the many pages that  require the same digital signature of the Approver in its own signature  block, for example.

You won't be able to use the same digital signature field many times accross that document though.

Each digital signature field is unique and Adobe Acrobat doesn't provide an easy way to work around what you're asking unless some heavy JavaScript scripting is employed.

You may be able to use other methods with JavaScript though, like employing the use of stamps, to name an example.