A digital signature is a cryptographic method to implement the above functions. In most cases the the signer owns a digital certificate and a private key. The private key is stored on a secure token or on a hardware security module (HSM). It is used to create the digital signature. The signer's certificate contains the corresponding public key and can be used to verify the signature.
Digital signatures are still not very widely used and the the knowledge about them is often fuzzy. This article tries to give an overview about this huge and complex topic.
Read more about digital signatures in PDF/A in our Expert blog.