Ed has an iPad 4 and he can't print to his Pixma printer. Apple says he can't. Leo says that Apple uses "AirPrint" to print via WiFi, and if the printer doesn't support it, then he'd have to add additional hardware to give it that support. But there may be software that Apple offers for free. Otherwise, Leo recommends xPrintServer. It'll take any USB printer and make it an AirPrint compatible printer.