After installation, open the PDF document with a reader. At this time, you can see the prompt box of digital signature. , black (blue) represents the verified digital signature, which is credible and effective.

Green represents an unverified but valid digital signature.

Red indicates that the digital signature is invalid (it may be that the document has been tampered with or the digital certificate has expired, and you will be prompted).

Yellow indicates that Adobe does not trust the digital certificate. (Maybe the partner didn't update the software. It is also possible that the signer made the certificate himself, rather than a trusted third party. ) Some signing certificates are integrated in various Windows systems released by Microsoft in advance, rather than in various softwares of Adobe, so it takes effect to call Windows integration, otherwise you may see a yellow prompt.

So how do you call the pre-integrated certificate in Windows? Click edit preferences for Adobe Acrobat Reader software.

Click "Signature"-"Verify ~ More"

Just select two check boxes in Windows integration. Reopen the document to see if it is still yellow, which means that this certificate is not trusted. Please contact the signer for verification.