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Obtain a digital ID, or create a self-signed digital ID in Acrobat. You must register your digital ID in Acrobat before you can use it. 

You can get a digital ID from a third-party provider. Self-signed digital IDs may be adequate for many situations. However, to prove your identity in most business transactions, you may need a digital ID from a trusted third-party provider, called a certificate authority.

Check with these third party providers:

http://www.digi-sign.com/

http://www.verisign.com/products-servic … index.html

http://www.geotrust.com/