Look on the
sourceForge there is a set of API's to generate PDF's... I am sure they can provide a least basic PDF viewing.
There was also a post on a javaranch forum about the different PDF viewer. The post was made by Benjamin LEONARD (an dammed good
java developper & more over a frien of mine). I remember he gave 2 package to do so !
Give also a look at the following :
www.pdfmachine.net InetSoft http://www.lowagie.com/iText/