The digital signature is simply a sequence of characters that is appended to the end of the body of a message to be transmitted under signature. It gives us the opportunity to inform, to faith and / or express a willingness in full legal compliance and security, without the need to be present for stamping on paper
our handwritten signature.
Digital signature uniquely identifies the person sending the message, makes sure that the message is exactly as it was issued at the time of receipt and that the signer does not have the opportunity to deny having signed the document. That is, a digital signature brings identity and integrity to a document and prevents repudiation at origin.
As examples of signed document standards, there is a PDF/A, which is a subset within the PDF standard dedicated to storage and long-term archiving of documentation.
There are also several certification authorities such as Chambers of Commerce, the Government, CryptoApplet (version free software developed by the University Jaume I) and so on.