Review annotations and comments are done in the "Review Canvas". Reviewers may make their annotations individually - on their own time - or you may also hold live real-time review sessions where multiple people may "whiteboard" on the content together or conduct more formal synchronized presentations (see "How do I hold a live presentation" for more details).
To annotate a Review
b - activate pencil tool.n - activate note tool.a - activate arrow tool.t - activate the text highlight tool.h - activate hand (pan) tool (or hold Shift key to temporarily activate it until released).z - activate zoom tool (or hold Option key to temporarily activate it until released).0 - zoom fit all; 9 - zoom fit width; 1 - zoom to actual size; 2 - zoom to 2x; 3 - zoom to 3xspace bar - start / pause videoleft / right arrows - advance to next / previous frame in video (or page for PDF files).up / down arrows - advance to next / previous file in review.x - toggles the mouse wheel action between vertical scroll and zoom. You can also press and drag the mouse wheel to pan.