Signatures are commonly used to authenticate documents. When you sign a physical document, you are authenticating its contents. Similarly, digital signatures are used to authenticate the contents of electronic documents. They can be used with PDF, e-mail messages, and word processing documents.
To digitally sign a document, you must have a digital ID. This unique identifier can obtained from various certification authorities on the Web, such as VeriSign and EchoSign. Once you have a digital ID, you can add register it with programs that support digital signatures, such as Adobe Acrobat and Microsoft Outlook. Then you can use the program's "Sign" feature to add your digital signature to documents.
The digital signature is simply a small block of data that is attached to documents you sign. It is generated from your digital ID, which includes both a private and public key. The private key is used to apply the signature to the document, while the public key is sent with the file. The public key contains encrypted code, also called a "hash," that verifies your identity.
Digital signatures can be used to certify or approve documents. Certifying signatures verify the document's creator and show that the document has not been altered since it was signed. Therefore, only the original creator of a document can add a certifying signature. Approval signatures can be added by anyone with a digital ID and are used to approve documents, track changes, and accept terms stated with a document.