Looking for a good tool to help you annotate files on Google Drive? Chalkup lets you post discussion prompts, add comments to discussions, distribute announcements and assignments and view files. Chalkup also provides a very good functionality called MarkUp annotator that allows teachers to easily annotate files and documents they receive from their students.
http://www.educatorstechnology.com/2015/03/good-way-to-grade-and-annotate-google-drive-files.html