Apple's answer to the question of printing on an iPad is to email documents to your Mac and print them from there. A number of software developers have created apps that attempt to provide the ability to print. But, only one developer has a solution that is the closest thing to being practical to use.
Avatron Software, creator of Air Sharing HD, has done a nice job of making it possible to print from an iPad. Basically, Air Sharing enables your iPad to print to printers shared by a Mac. And, it doesn't require any additional software installed on your Mac. (Help topics in Air Sharing HD tell you how to share a printer.)
Printing Files in Air Sharing HD
The primary features of Air Sharing HD are file sharing and file access. You can access files on your Mac and online servers, such as iDisk, over a Wi-Fi network. Copy files from your Mac to your iPad. Or, connect to the iPad from a Mac to transfer files to it - without having to install additional software.
Most file types copied to Air Sharing HD can be viewed, as well. And, any files that can be viewed, can be printed, too. Air Sharing supports viewing and printing of many common document types, including Microsoft Office, iWork, PDF, text, photos and other image files.
To print a document, view it in Air Sharing. Then, tap the icon in the lower-left of the screen and select Print. A list of any shared printers the iPad can see on the network is displayed. Tap the printer you want to print to. You'll be able to select a range of pages in a multi-page document to print, too.
The resulting print-out isn't always perfect. Often, the layout, font or pagination are not as they are in the original document. Still, when you really need a paper copy of something, Air Sharing does a satisfactory job of it.
Printing Email Attachments
There are two ways to print an email attachment. And, it depends on the type of attachment it is.
Generally, if the attachment is a document, such as a Word, Pages or PDF file, you'll be able to open it in Air Sharing HD to print it. In the email message hold your finger down on the attachment icon. A menu will pop-up. Tap "Open in...", then tap "Air Sharing". The document will be copied and opened in Air Sharing for you to print.
If the attachment is an image or text file, it takes a little more effort to print them. Air Sharing provides the means of accessing an email server as if it is a file server. You then navigate to the email message using the built-in file browser and open the attachment to print it.
Printing an Email Message
As described above, open the email server as a server. Navigate to the email message. It will be listed as a text file. Open to view and print it.
Printing From Pages, Numbers and Keynote
Unfortunately, Apple doesn't provide a way for developers to directly open an iWork document from another app. So, you'll have to mail the iWork document to yourself. Once it is in your Mail Inbox, print it as described above.
So, as long as you can get a document you wish to print into your email inbox or on a server that Air Sharing can access, you'll be able to print it.
While printing from an iPad isn't anywhere near the way we'd really like it to be, it's good to see apps like Air Sharing HD fill in the gap (as best as they can, anyway).