•To zoom in a document, click the Zoom In 
button on the toolbar, or press CTRL+PLUS SIGN.
•To zoom out of a document, click the Zoom Out 
button on the toolbar, or press CTRL+MINUS SIGN.
To zoom in or out of a document, you can also hold down CTRL and rotate the mouse wheel.
Use the Magnifier Tool
Use the Magnifier Tool 
to switch between 100% and "fit whole page" views. Simply click anywhere in the document, to toggle views.