I have been reading the manual that was linked and, unless I am missing it, it appears that you have to use the Digital Paper App in order to transfer documents to and from the device. This would seem to imply that the RP1 is not seen as a mass storage USB device by the operating system. Hope I am missing something.
UPDATE: on this page
http://helpguide.sony.net/dpt/rp1/v1...001178339.html
it says:
"To transfer documents between a computer and the Digital Paper (DPT-RP1), the Digital Paper App must be installed on the computer."