You can add shape annotations in the form of straight or free-form lines, squares or rectangles, and circles or ovals.

• Click the desired annotation tool button—Line  to draw a straight line, Pen  to draw a free-form line, Multi Shape  to draw a few free-form shapes at the same instance, Rectangle  to draw a square or rectangle, or Oval  to draw a circle or oval—and draw the shape on the image. In the dialog box that appears, type the required text, and click Create.
  
  Notes:
• Press the Shift key to keep the straight line perfectly horizontal or vertical.
• Press the Shift key to create squares or circles with the Rectangle and Oval tools.
• Use the Multi Shape tool to mark a few items at the same time, when you complete drawing the shapes, click Done and type the required comments.