With the most recent iOS on your iPad, iPhone or iPod Touch you can use AirPrint to print a document from some apps to some printers. Find out which printers are compatible and how the printing process works.
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Apple’s list of printers that support AirPrint is here. They also have a AirPrint Setup and Troubleshooting guide.
Here are three Mac applications that allow you to turn your Mac-connected printer into an AirPrint device that your iPad can print to: