Preview is Mac’s default app for viewing files such as PDFs, JPEGs, PNGs, and most other image files. Preview has tools that allow you to draw shapes such as arrows, stars, and rectangles onto your image. You can even mask or magnify part of your file. This allows you to annotate your file visually.
Use Mac’s Preview App to Draw Shapes and Images on a PDF Document
1.Open the PDF file in Preview, and then open up the Markup Toolbar by clicking the toolbox icon
 from the main toolbar. 
2.To add a shape, click on the shapes icon 
 in the markup toolbar. The main shapes are a line, arrow, rectangle, round-cornered rectangle, circle, speech bubble, star, and polygon. The two advanced shapes are the Mask 
 and Loupe
 shapes, which are used to focus in on an area. The Mask will create a rectangular area. Everything outside the area will be darkened but still legible. The Loupe will create a circle that magnifies everything inside of it.
3.The shape you select will appear in the center of your PDF. To move the shape, click on it once to select it. Hover your cursor over the edge of the shape; it should change to a grabbing hand. Click and drag your shape.
4.To resize a shape, select it, and then click and drag one of the blue handles. The polygon and star shapes have green handles that allow you to change the number of points. The arrow and line have a green handle that allows you to bend the middle point.
5.You can change the thickness, style, and add shadow to your border by clicking the shape style 
 button to the left of the border color tool. 
6.To change the color of your shape’s outline, click the icon with the hollow square 
 and choose a color. The white square with a red slash through it 
 denotes a clear.
7.To change the fill color, select the shape, and then click Fill Color from the markup toolbar as shown below. The white square with a red slash through it  denotes a clear background.Â
