Something to help with school work for a physically disabled child that has an extremely hard time writing.

Looking for an app where you can take an image file (tig gif, jpeg, bmp, pdf, etc...) be able to use the whole Touchpad screen, zoom in / out and have the ability to write / draw over the image and erase part of what was drawn. For example, teacher could email math homework image file with all the math problems, student would be able to zoom in, work the problem with their finger, zoom out, and then zoom in on the next problem, save the updated image file and email back to the teacher.

I've looked for an app like described above but was not able to find any that came close. Using the whole Touchpad screen and being able to zoom in / zoom out are REALLY needed.