This article walks you through the process on how to disable this feature.
By default all Signed PDF files are sealed with a randomized password so they cannot be modified.
Document encryption is governed by a back-end setting that success or support can change to a password of your choosing.
Contact your success manager (or submit a support ticket) with your request to install a known password for your account, and include the password you would like to apply (letters and numbers only, no special characters).
This PDF sealer password is applied when the PDF is downloaded (or attached to the final email), so any new password value is only applicable to PDFs that are downloaded/attached after the password is installed.
Once the unlock password has been installed, you can follow these steps to unlock the PDF file:
You can now make any edits to the file.