You'd like to include a 3rd party JAR in your NetBeans Platform application. It would then also be handy to be able to read the related javadoc in the NetBeans Java Editor and to browse from there into the sources of the JAR.
How to do this? I figured out a solution today. (It will be much better & smoother in 7.1, where absence of sources upon request will prompt you to assign sources for the JAR.)
As an example, I'll take the interesting looking xmlworker JAR (apparently lets you convert XML to PDF) from the iText project.