The Preview app included with Mac OS X does more than just open images and PDF files. While the program can zoom in and out of open PDF files (and even display the document in a full-screen view), the Smart Magnify feature in Preview for OS X 10.7 (and later) enlarges a specific area of the document quickly.
To use the Smart Magnify feature, open a PDF file with Preview and press the tilde (~) key on the keyboard. When the magnification window appears, you can slide it up or down by using the keyboard’s arrow keys or by moving the mouse. Tap the tilde key again to close the Smart Magnify window. Apple’s site has instructions for using all of Preview’s many features, including scanning, cropping and rotating images.
