The following instructions pertain to the Print to PDF feature in Acrobat on both PC and Mac computers.
An Adobe Sign PDF has a certified signature and that certification conflicts with Interfolio's system. In order to upload an Adobe Sign PDF, you must strip the certification by using Print to PDF, which creates a copy that is compatible with Interfolio. This Print to PDF copy can be uploaded to Interfolio.
The following link contains information from Adobe about Print to PDF: https://helpx.adobe.com/acrobat/using/print-to-pdf.html