why the signature is invalid?

I'm using acrobat reader(version:20.012.20041.1044) on windows 10.

I found a special pdf document that after sign multiple, just only the last signature is valid when opened with adobe reader.

I valided it on docusign and https://account.ascertia.com/demos/PDFSignatureVerificationStep1 / https://www.pdf-online.com/osa/validate.aspx .

No one tell me signature is invalid, just certificate is not trust.

I don't know why adobe reader tell me signature is invalid.

Pleasy help me, thx!