I am sick of having to print out all the PDFs of course readings to bring into class so I can add notes to them. I know that there are apps out there that let you highlight text in PDF files for later reference. The trouble is, a good portion of the PDFs that are given to us are not text, but scanned pages out of old textbooks, so an app that just has 'text highlighting' will not suffice. Are there any apps that allow you to draw on and save PDF files that are images and not text?