I have been using a different solution. The instructor can open the written assignment by clicking on it. Whenever the instructor wants to add a comment s/he clicks in the document, hits ctrl-U (Mac cmd-U) to start underlining and types inline comments. When the instructor is done grading the paper, s/he hits ctrl-A (Mac cmd-A) to select the whole text, then uses copy & paste to put the commented paper into the comment box beside the grade. The underlining goes thorugh the clipboard so the student sees that as the clue that it is a comment. That leaves the student with the paper in its original form as submitted as well as the ability to read instructor comments in context.
I will look at "upload and review", though.
Bruce