Hello, @rwilliamson
Welcome to the DocuSign Community!
On this case, if the envelope is in the Status of Completed, the best thing to do is to create a new envelope, add the document again, add you and your client as recipients, add the Sign Here and other fields in the document then send it. Thus, at the end a certificate of completion will be generated with all audit details and info from the signers.
If the envelope was in the Waiting for Others status, you could correct them, add yourself as a signer then send again.
I hope that helps!
Alexandre
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