Since I think handwriting should not be underestimated and encourages hand-eye coordination, I downloaded a free app called neu.Annotate PDF. It allows handwritten annotations as well as typed text. Further, pages can be mailed as PNG, JPG and PDF, saved to photos and opened in Dropbox, iBooks, Adobe Reader etc. Shapes and highlighters, wrist protection, the ability to delete pages, insert pictures or new pages leaves little to be desired. Only the button to increase the width (of lines, fill or text) and change the colour was difficult to find for students (it appears when you click on one of the pens).
Link to app
by neu.Pen LLC