What is "timestamp embedded in the document"?

Hello,

I have a PDF file that contains a signature with signature timestamp (I guess it is called in Reader "timestamp embedded in the signature") and also a timestamp embedded in the document. But I don't know what it means. Specifically what kind of timestamp it is..

It is not a document timestamp (archive timestamp) because it would be recognised in the Reader separatelly next to the signature.

What kind of timestamp it is?

Thank you.