How are Documents Routed for E-Signature?

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How are documents routed for E-Signature?  Apparently, documents for signature are emailed to each recipient through 'adobesign@adobesign.com'.  This is fine for most applications, however, are there any protections for sensitive documents such as company proprietary information?  Specifically, are the documents and information stored or read by Adobe? 

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No one knows?