From locklizard's
page about their PDF security, it sounds like the actual files reside on a server, and are accessed through special software, not copied to the viewing computer at all. In that case, they'd only be readable when the computer is online, and not transferable to mobile devices.
(Or maybe the encryption key is tied to the web if the copy is not. It's hard to sort out exactly what they mean, and I suspect some of that is deliberate.)