How to unlock a PDF after Adobe Sign has been used

Hi,

I am trying to work out if it's possible to unlock a PDF once Adobe Sign has been used.  I used Adobe Sign to help get two witness signatures.  Got the PDF back and sent back to the original requester.  They complained that they could not make a copy (I assume this is because the PDF was locked after Adobe Sign was used).

I read this article: https://helpx.adobe.com/sign/kb/unlock-a-signed-pdf-file.html  to see if anything like this was possible and it seems there is a way?
I'm not sure how true this is or how to install a known password on your account - the support bot can't get anywhere close to helping with that.

Any help or tips would be appreciated 🙂