We are having a discussion at work about the validity of having more than one Adobe Digital Signature using Adobe Acrobat Standard DC (version 2015.006.30527).
We are adding in multiple digital signatures on one document by adding in signature fields using the Prepare Form functionality or by adding a digital signature, and then "Clear Signature" to create multiple empty digital signature fields for users to digitally sign. This enables us to put multiple digital signatures on one document. Once signed, the audit trail on the Signature Panel shows all green checkmarks with no errors which indicates that all signatures are valid.
My colleague is saying that multiple digital signatures on one document does not provide for "valid" signatures since "there is a limitation that it (Adobe Acrobat Standard DC) only allows for one “legal” signature – the last person who signs and “seals” the document by saving it as pdf. The PDF is time stamped and digitally encoded via Adobe." Therefore they are saying that only the most recent signature on the document is valid and all other previous signatures are not valid.
I don't believe the above is correct since all signatures and certificates show as valid in the Signature Properties tab.
Any thoughts on the above? As far as I can see, all of the signatures are valid and Adobe Acrobat Standard DC is capable of adding in multiple digital signatures on one document (even "legally").
I don't know whether the process by which you create documents with multiple signature fields is ok. If you provide an example with multiple signature fields as applied by your process, we can take a look and discuss that.
First of all, though: You call those signatures "Adobe Digital Signature" and discuss whether "Adobe Acrobat only allows for one legal signature." Those signatures are not owned or currently defined by Adobe, instead they are specified by ISO and other international and national standardization institutions. And Adobe in particular does not decide which signatures are legal, that is up to your applicable legislation and may or may not follow industry best practices.
Technically there are two main multi-signature-field cases to differentiate:
Multiple signatures applied sequentially: Specifications commonly use this procedure for technically valid signatures.
Multiple signature field widgets of a single signature value: This is discouraged by specifications; most ways to create such constructs actually are forbidden.
Concerning the legal value let me state that I'm not a lawyer. From experience, though, technically valid signatures usually also are legally valid as long certain additional, non PDF-specific requirements are fulfilled.
Be aware, though, that between applying signatures it may be allowed to apply certain other changes to a document, in particular form fill-ins, sometimes even adding/changing/removing arbitrary annotations. Here of course a signer only signed the document in the state he saw it and only is responsible for the contents at that time, not for changes after his signature.
A document can be prepared in a way that form fields a certain signer is responsible for are locked when he signs. Making use of field locking might be necessary in your use case.
I agree that your preparation process seems open to question: sign then clear then sign again? Why?
Multiple signatures are entirely viable and trustworthy. If the file is changed after signature A and B and before signature C and D then only C and D will be valid. But the legal status may be an entirely another matter; this depends on the laws in effect in the country, state or region where the document is prepared, and you need to consult a specialist lawyer.
There is a general rule: one person should NEVER sign more than once. We often see fatally flawed workflows where people believe they are "signing pages". Such misdirection may leave the signature invalid, since the signer was so badly informed.