Several questions about SignatureField and Signature

I have several questions in the process of learning Aspose Library. 

First is, in a PDF, we would probably have a certificate chain, that means we can have more than one certificate. But our SignatureField.ExtractCertificate() can only have one stream as return value. so how can we got multiple certificates from it?

Second is, is the return value Signature.Verify() Method verify all the certificates  is correct?

Thanks a lot