Hi Colin,
I have only used iText a couple of times but I am pretty sure that one has to save the file to view it, I am happy to be corrected if I am wrong. I used it when generating report files and receipts, so we had to store them anyhoo, but I seem to remember it has to be stored to be viewed.
On saying that though, I have just found this link, it shows PDF being generated to a HTTP request,
webpage , but it is still writing the document to an OutputStream, so I don't really think this will help.