Signed and all signatures are valid, but with unsigned changes after the last signature.

Hello,

After filling in a PDF form, validating, and then digitally signing it, I initially receive a green check message  saying "Signed and all signatures are valid." Great! But after closing and opening the same PDF I receive the following message with a yellow triangle: "Signed and all signatures are valid, but with unsigned changes after the last signature". When comparing the Signed and Current versions, there are no discernible changes to be seen.

I have tried other solutions mentioned in similar threads, but none have worked for me so far. I made sure to update my Adobe Acrobat to the latest version and update the AATL certificates in Trust Manager under Preferences. Also, due to the nature of the PDF, I do not have the admin rights necessary to modify the signature field properties in the Prepare Form section, so I cannot alter the signature field properties to Mark as read-only. 

Kindly asking for your support to prevent any such changes after digitally signing!