I have an Air 1.5 application that displays local files in an <mx:HTML> control. The keyboard PageDpwn and PageUp keys move up and down in a directory seting the html.location to the new file name. This works fine with html, swf, and txt files but when a pdf file is loaded, the pdf grabs the keyboard events and prevents my AIR controller from getting the KeyboardEvent.KEY_DOWN events. So you're stuck in that one file.
If I make the window bigger than then html control and click outside the pdf file, I get keyboard focus back. But this isn't a practical solution; having to click defeats part of the purpose of the application.