The Encryption service lets you encrypt and decrypt documents. When a document is encrypted, its contents become unreadable. An authorized user can decrypt the document to obtain access to the contents. If a PDF document is encrypted with a password, the user must specify the open password before the document can be viewed in Adobe Reader or Adobe Acrobat. Likewise, if a PDF document is encrypted with a certificate, the user must decrypt the PDF document with the public key that corresponds to the certificate (private key) that was used to encrypt the PDF document.