Of course the drawing will run slow. PDFs are just a container for many different types of stuff (images, postscripts, etc) there could be all sorts of thigs inside that PDF that are slowing down AutoCAD.
I second mhupp's suggestion.
I'm not sure how the WSL will help AutoCAD in this case, d2010. I mean as far as I know, AutoCAD itself is reading the PDF contents; it doesn't use a system viewer does it?