Preview is an app that's been around for so long we Mac users utterly take it for granted; it's the app included with OS X that enables us to display image files and Portable Document Format (PDF) files by double-clicking on them. If you have no other image editing or cataloging software on your Mac, Preview can often open the image file you're trying to use. That's because Preview uses technology embedded in the core Mac operating system — things like Quartz, ImageIO and CoreImage frameworks — in order to do its thing. The list of supported file types is impressive, and you can do simple editing with them too: rotate, resize, and crop, add shapes, copy and paste in other applications. You can also scan documents in Preview, if you have a scanner available to your Mac (including many network scanners), and you can even use Preview to store a digitized copy of your signature to embed in PDF documents.