About digital signatures

A digital signature, like a conventional handwritten signature, identifies the person signing a document. Unlike a handwritten signature, a digital signature is difficult to forge because it contains encrypted information that is unique to the signer. It can be easily verified and informs recipients whether the document was modified after the signer initially signed the document.

To sign a document, you must obtain a digital ID or create a self-signed digital ID in Acrobat or Adobe Reader. The digital ID contains a private key and a certificate with a public key and more. The private key is used to create the digital signature. The certificate is a credential that is automatically applied to the signed document. The signature is verified when recipients open the document.

When you apply a digital signature, Acrobat uses a hashing algorithm to generate a message digest, which it encrypts using your private key. Acrobat embeds the encrypted message digest in the PDF, certificate details, signature image, and a version of the document when it was signed.

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Digital signature in a PDF form

Additional resources

For videos and articles on digital signatures, see these resources: