Hi Joel,
Glad to hear you have resolved the problem. Once you experiment with marking directly on submissions, you will probably wind up using it more and more. At least I did before I retired. With my MS Surface Pro and pen, it was like grading "papers" again, which for me, just seemed to go faster than trying to type an explanation of what was wrong with a submission, be it writing, pictures, drawings, spreadsheet, etc., or anything else that could be converted to PDF.