Adobe acrobat reader 7.0 User Manual

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Document security and digital signatures
With Adobe Reader 7.0, you may receive an Adobe PDF document with attachments that 
are bundled into a secure electronic envelope (eEnvelope) designed to protect documents 
during transit. When you open the eEnvelope, you can extract the file attachments and 
save them to disk. The saved files are identical to the original file attachments and are no 
longer encrypted when saved.
Acrobat 7.0 users can create Adobe PDF documents using security policies that can expire 
and revoke documents, as well as maintain accountability by keeping track of who opens 
protected documents. You can only open these secure PDF documents if you have the 
necessary passwords or are on the list of approved recipients.
You can sign a PDF document only if the document includes additional usage rights 
assigned by the creator of the document.