Testing undo and redo buttons: Create a new assignment. Enable 'File submissions' are 'Submission Type' section, and 'Annotate PDF' in 'Feedback Types'. As a student user, submit a multi-page PDF file to the assignment. As a marker, view all submissions and 'Grade' the submission uploaded in the previous step. When the PDF annotate tool appears, use the pen or line tools to at least one annotation to the PDF. Use the 'undo' button on the toolbar to remove the annotation. The annotation should be removed from the document. Use the 'redo' button on the toolbar to reintroduce the annotation - it should reappear in the document (in the same location and with the same properties).