From Adobe's description of the new feature:
"The initial release of Adobe Reader Protected Mode will be the first phase in the implementation of the sandboxing technology. This first release will sandbox all “write” calls on Windows 7, Windows Vista, Windows XP, Windows Server 2008, and Windows Server 2003. This will mitigate the risk of exploits seeking to install malware on the user’s computer or otherwise change the computer’s file system or registry. In future releases of Adobe Reader, we plan to extend the sandbox to include read-only activities to protect against attackers seeking to read sensitive information on the user’s computer."
email: david @ sharpesecurity.com