1. Enter reading page ->  Tools; 

2. Select  Freehand on the toolbar;

3. There you can change the Color and Line Width on the side panel;

4. And a eraser is available to erase the undesired annotations, a ruler and a protractor are provided if you need to draw a line or a circle;

5. Click Done when you finish your freehand drawing;

6. To remove the annotation, right click the annotation and select Delete.