Not sure about printing a whole PDF, but for text or an image, under iOS 6 (which most iPad users have by now), you can use GoViral from Milkman Games.
With that you can do a generic message with image attached, and it will open up the iOS sharing panel, and you can AirPrint from there.
The number of AirPrint compatible printers, or users that are set up to print that way, is not so high though, so you could use GoViral to also email the image to a computer in order to do the printing.
Hi Colin, thanks for answer, but forget to mention that I need to do call print programmatically from Adobe Air. E.g. can I call AirPrint from Adobe Air ? or can I launch external application from Adobe Air ?
It's neither thing really. In AIR you give the user a Share button, that brings up the sharing dialog as an overlay. From there the user can tweet it, send it to Facebook, save the image, or AirPrint it. Once printed the dialog goes away and you're still inside the AIR app.