I want a device with a large screen (as big as possible to ease reading), that will display PDF files in a user friendly format so I can read/study from my collection of science PDF books.I usually have a pen and paper to work/study as I read from the device. It has to be a portable device, yet display the PDF in a big size. What device can you suggest? Of course a notebook can be used, but it's not as comfortable as a tablet like the Kindle. However, I read that the Kindle sometimes has some trouble displaying PDF's. Also, it'd be nice to be able to plug the device to AC power for long study sessions.Any suggestions? Thanks.