How to solve ’no valid signature found in this submission'

Question

Why the signature certificate of the PDF indicates “There is no valid signature found in this submission”?

Answer

A signature certificate is produced only when the form knows who was asked to sign. Check these in order:

1. The form was filled in from an invitation link with Signature Certificate turned on, or from a workflow step with Create signature certificate on. A form filled in from its public link never produces a certificate.
2. The Signature field was actually signed before the form was submitted.

Forms created before the certificate was upgraded: a Signature field that was left off the certificate earlier cannot be added back, because no form builder shows the Collected to Signature Certificate option any more. Clone the form instead: the copy gets the current certificate, which covers every Signature field.

Discover signature certificate

You can discover more about signature certificate here.