Versioning
From time to time documents need to be versioned, corrected, and then redeployed.  This is easily performed but what about the documents that have already been downloaded and saved by an end user?  These documents remain out of date, uncorrected, and may continue to be distributed. 

The premium Acrobat.com Live! PDF service would provide users with the ability to embed a special "live" feature into their documents that enables the document to reach back to the Acrobat.com server to ensure that it is the most current version of the document. If the document has been updated the user will be prompted to download the new version of the content ensuring the content is up to date.

Social Commenting and Markup
In addition to the version capability the original author of the document will be able to allow "Social Commenting".  With Social Commenting enabled anyone with an Adobe ID will be able to comment on the document. Those comments will be sent to the controlling author(s) for moderation.  Those comments can be changed, approved, and then included in the document.  Those approved comments will be retrieved by anyone opening the PDF document.