A digital signature is an electronic signature that is used to authenticate the identity of the sender of a message or the signer of a document, and possibly to ensure that the original content of the message or document that has been sent is unchanged.
Digital signatures are easily transportable, cannot be imitated by someone else, and can be automatically time-stamped. It has the ability to ensure that once the original signed message is received, the sender cannot easily repudiate it later.
A digital signature is used to authenticate the identity of a user and the document's contents. It stores information about the signer and the state of the document at the moment of signing.
It is a base class that provides the functionality to create either visible or invisible signature on the page. To create an invisible signature, just set zero signature size. Later, the visibility of the signature is verified by using the Visible property. PdfDigitalSignature contains information about signer, signing location, signing reason, and so on.
When you use digital signatures, each user is given a digital certificate. This certificate is actually a small file on a disk or on another device, such as a smart card. Each certificate also contains a unique code, and the certificate imprints this code on each signature you create with it. This means that all of your signatures can be traced back to your certificate, and the certificate itself can be traced back to you. In this way, digital signatures identify you through a clear chain of ownership.
It is a class that provides the functionality to use certificates for PdfDigitalSignature from PFX files or local Certification Storage. Certificates in local storage are found by using static methods FindByIssuer, FindBySubject, FindBySerialId. Also, there is the GetCertificates static method, which allows to get an array of all certificates from the local storage.
PdfCertificate class is used for getting the certificates from disk and PdfDigitalSignature class is used to sign a document with the given certificate. PdfDigitalSignature class has methods and properties that allow to set the signature information such as reason, location information, bounds where the signature has to be placed, and contact information.