esignature validations

There are many ways to apply an e signature to a PDF.

There are a number of on-line services where you use a secure logon to access the service and then upload the PDF to the service and have the service either distribute or let authorized users access the file. For this type of service the service provides the authentication and records to show the file has not been altered since was made available.

Within Acrobat and Reader there is the user's digital certificate This digital certificate has a private key and a public key. The signer uses his private key to apply his/her digital certificate to the PDF and then in a very secure way, usually a separate email, send the public key to those who need to validate the signature or certificate applied to that PDF. The use needs a pass phrase or password to use the private key. Other users only need to import the public key certificate into their copy of Acrobat or Reader.

You might want to access Adobe's site and learn more about digital certificates and signatures.

Both methods are approved by many countries for digitally signing contracts and other legal documents.

http://www.adobe.com/cfusion/search/index.cfm?term=digital+signatures&loc=en_us

Digital Signature documentation on Adobe.com