I have an idea of what this browser add-on does.
Adobe PDF Browser Control (AcroPDF.dll)
Apparently, if I disable this one, PDFs embedded in a page with the embed or object tag fail to function properly. So, its pretty clear as to its function.
However, I can't find anywhere accurate documentation on what this add-on below does.
Adobe PDF Link Helper (AcroIEHelperShim.dll)
IE9 (with Reader X) seems to work flawlessly with it disabled. PDF's still open within the browser. Only if I uncheck Display PDF in Browser in Readers preferences does that cease. I played around on an XP VM with IE7 and Reader X... no isssues noticed when disabled.
Does anyone know the purpose of this add-on? At one time I believed it was necissary for the 'within browser' functionality to work, though that was never verified. Something change?