iAnnotate supports printers using Apple's driverless AirPrint protocol for iOS apps. For more information about AirPrint, consult Apple's support page on the topic: http://support.apple.com/kb/ht4356
How to Print from iAnnotate
iAnnotate contains two dedicated buttons for printing. From the Document section of the Toolbox, you can select either Print or Print Current Page. "Print" prints the entire document or just the annotated pages, while "Print Current Page" prints only the current page.
Alternatively, you can tap the document's tab and choose Print from the resulting popup menu. This method only gives the options to print the whole document or just the annotated pages. You cannot print the current page only from this menu.
Lastly, you can print a document from the Actions accordion. Tap Actions > More Actions > Print. From in the Library, you must select the document via its selection circle before using this command.
Flattened vs. Original
Upon choosing to print a document, iAnnotate will prompt you to select either Flattened or Original.
Flattened prints the document with all of its annotations compressed (or "flattened") into the document. Popup annotations like those made with the Sound Clip or Photo tool are not compatible with flattening, either during printing or emailing. Original prints the document in its original form, with no annotations.