The Multivalent Browser is a Java-based browser that can natively
display PDF, HTML, UNIX man pages, DVI, and more. These viewers can
now be embedded in your Swing-based application. The source code of
the class multivalent.devel.Embed demonstrates how.
Viewers are free for any use and open source.
More information and download instructions:
http://http.cs.berkeley.edu/~phelps/Multivalent/