Hi Mikel, indeed you are correct. Unless the PDF also has an open password set, using 3rd party software you can refry the signed PDF from Adobe Sign.
However there is a better for users with business/enteprise type of Sign accounts. These Sign accounts can be configured so the sealing is changes so the signed pdf no longer has an owner password, and uses a digital signature rather than a certitifcate to seal the Signed PDF,
with such a PDF, Acrobat can be used to easily remove the seal by combining the file (but not selecting other files if not actually wanting to combine) into a new file, or extract all pages into a new file. This unsealed copy can be redacted, or otherwise be processed. Though it's advisable to also keep a copy of the sealed pdf version as well.