It's trivial to set Adobe Reader to open outside the browser. Just clear the "Display PDF in browser" check box on the "Internet" panel of the preferences.

Multiple resolutions in one file was one of the features of the FlashPix format that was introduced way back in 1995. There was a complete ecosystem offered by major tech companies, including free browser plugins that provided zooming and as-needed download. FlashPix failed to gain a significant foothold and is rarely used today. There's a little bit of information on the format at http://en.wikipedia.org/wiki/Flashpix, and a format specification at http://graphcomp.com/info/specs/livepicture/fpx.pdf.