While this feature isn't available, (I would like this capabililty also), you can have a pdf open in 'pdf to go' on the lcd side while reading something else on the ereader side. However, 'pdf to go' is a read only app (no editing features outside of copying text, afaik). Perhaps a developer will create an android pdf editing app in the future?

As I work with a lot of public domain material (and sometimes my own material), another feature I would like is the ability to move or export pdf's that I have annotated on the edge with all of that intact so that I can read and edit outside of the ereader as well. Presently, you can export but it is converted to an image pdf and if you move your original pdf file out of the library or the Adobe Reader environment, you lose all of your previous editing. This is an Adobe related issue having to do with drms and publishing rights, so I don't think I'll be holding my breath waiting for it anytime soon. Also, I make sure I keep duplicate copies on my desktop pc.

I work around this issue by exporting my annotations (pdf image files) and journal notes and using those to edit the original pdf in an editor on my pc. Quite a lot of work but I've found it to be a fairly effective 'study tool', as well.