I have encountered several cases of PDF documents in the past few years. When I signed the first signature, Acrobat DC verified the signature correctly, but when I added the second signature (even though the second signature was signed with Acrobat DC) , Acrobat DC will report that the previous signature is invalid, but I didn’t actually make any changes. Other PDF software (Acrobat 9.0 Pro/iText/Foxit) can verify these signatures correctly. I don't understand what causes the Acrobat DC verification to fail?

In addition, I also encountered a "1 miscellaneous change(s)" problem in Case1.pdf

Use the latest Windows 10 and Acrobat Pro DC v2021.007.20091 to reproduce this problem, and Acrobat Reader DC can also reproduce the problem.