Sigh... it shows up as "No security" in acrobat 9 pro. I had to install the free Acrobat reader on a virtual machine to be able to see what you can see.
I don't understand why comments aren't being allowed - our PDF output library lets us explicitly forbid "annotations", but there's nothing to turn them on. They're assumed to be allowed by default. I guess I will need to investigate this a bit more.
