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Chapter 9: Digital signatures
You use a digital signature much like a handwritten signature—to approve documents. A digital signature verifies your
identity and may include a photo, an image of your handwritten signature, or other personal details that you choose.
Document authors can attest to the contents of their documents by adding a certifying signature.
Digital signatures
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 and easily verified.
Most digital signatures are referred to as approval signatures. Signatures that certify an Adobe® PDF are called certifying
signatures. Only the first person to sign a PDF (most often, the author) can add a certifying signature. A certifying
signature attests to the contents of the document. It also allows the signer to specify the types of changes allowed for
the document to remain certified. Changes to the document are shown in the Signatures panel.
To sign a document, you must obtain a digital ID or create a self-signed digital ID in Adobe Acrobat®. The digital ID
contains a private key and a certificate (or public key). The private key is used to add the digital signature, and the
certificate that you share with people who use it to validate your signature.
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, along with details from your
certificate, an image of your signature, and a version of the document at the time it was signed.
Note: For the latest information about digital signatures, choose Help > Online Support > Knowledgebase to open the
Adobe Acrobat support page on the Adobe website. Then search for "digital signatures."
Digital signature in a PDF form
For articles on digital signatures, see these resources:
• Digital Signatures in PDF and Acrobat:
• Migrating and Sharing Security Settings:
• Adobe Acrobat 9 Digital Signatures, Changes, and Improvements (PDF):
www.adobe.com/devnet/reader/articles/reader_compatibility.html
More Help topics
"About digital
IDs" on page 247
www.acrobatusers.com/tutorials/digital-signatures-pdf-acrobat
www.adobe.com/devnet/acrobat/pdfs/sharing_security_settings_90.pdf
Last updated 9/30/2011
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