Humanities instructors: What's the simplest tool for students to make marginal notes on a PDF and read one another's annotations? I don't want something fussy like #Hypothes.is or #Perusall -- am not grading them on these, just want them to be able to read over each other's shoulders. I've used Google docs for text files, but is there an equivalent for PDFs (OCR only I assume)? Thanks for any advice! #teaching #annotation