Preview is one of the great, bundled applications built into Mac OS X. It’s an application I use daily. On most Macs, Preview is the default image and PDF viewer. Preview gives Mac OS X the ability to open a wide variety of image files straight out of the box (listed below), and it also offers basic image correction tools, cropping and rotation tools and annotation tools for PDF and TIFF documents.
However, I mainly use it to convert graphic files from one format to another. Typically I am converting a PDF to a JPEG or PNG file, but sometimes I also use it to convert a graphic file to a PDF for easy sharing with other people. You can also use Preview to convert images to the Photoshop file format, as well as to JPEG, PICT, BMP (for sharing files with PC users), PICT, Targa (for video), and more.
To do this, open the file in Preview, go under the File menu, and choose Save As…, where you can export your graphic in your chosen format. If the format you’re saving in has options (such as quality and compression settings for JPEG and TIFF images), they will appear near the bottom of the dialog.
Preview employs Apple’s implementation of Adobe’s PDF specification, and makes significant use of Apple’s Cocoa graphical user interface, Quartz graphics layer, and QuickTime image codec. Preview can open popular file types such as PDF, PNG, GIF, PICT, EPS, JPEG 2000, JPEG, RAW, TIF and TIFF, and BMP (Windows Bitmap files), along with less common file types such as DNG (Digital Negative files), FAX (faxes), FPX (FlashPix files), HDR (High Dynamic Range Image files), ICNS (Apple Icon Image files) ICO (Windows icon files), OpenEXR (OpenEXR files), PS (Adobe PostScript files, after an automatic conversion to PDF), PSD (Adobe Photoshop files), PNTG (MacPaint Bitmap Graphic files) QTIF (QuickTime image files), RAD (Radience Scene Description files), SGI (Silicon Graphics Image files), TGA (TARGA image files), XBM (X BitMap files),
Learn more about Preview by clicking here