For some reason, the read-only protections placed on documents downloaded from the internet result in keyboard bindings like page-up and page-down from being disabled.

I routinely use the keyboard to navigate documents, which has the result that I routinely have to click the 'enable editing' button when reading a downloaded document. This renders the read-only feature fairly useless as a result.

Would it be possible to make sure that basic keyboard navigation still works with downloaded documents, somehow?

There are aspects of this that make it a security issue, since it leads people to click 'enable editing' when they otherwise wouldn't need to.