JEditorPane does not support PDF at the moment. of course you could implement your own EditorKit for it (like HTMLEditorKit and RTFEditorKit). Might not be that easy, though.
Another way would be to use the acrobat reader plugin if it is possible to start a web plugin inside the java virtual machine. Or to start the acrobat reader using Runtime.exec().
If you are only interested in the contents of the pdf and don't care much on shwoing the layout, there are open source pdf parsers that allow you to extract and modify the contents (and even the layout). See iText (
http://www.lowagie.com/iText/).
chantal