I got some excellent help from Mark Stephens, who is from IDR Solutions, which produces JPedal. Using the LGPL version of JPedal, and code provided by Mark, it's now possible to right-click the node that appears in the Presentation Window:

...after which, using a file browser (to locate a file on disk) or a URL (a very simple check is done, the URL must start with "http" and end with "pdf"), you can now open PDF files as images (thanks to conversion from PDF to images done by JPedal) into NetBeans IDE, typically (I imagine) for presentation purposes:

Note that you should consider the plugin in "alpha" state. But, despite that, I've had good results. Try it and use the URL below, as a control test (since it works fine for me), which produces the result shown above:

http://edu.netbeans.org/contrib/slides/netbeans-platform/presentation-4-actions.pdf 

However, for some PDFs, the plugin doesn't work, and I don't know why yet (trying to figure it out with Mark), resulting in this stack trace:

java.lang.ArrayIndexOutOfBoundsException: 8
   at org.jpedal.objects.acroforms.formData.SwingData.completeField(Unknown Source)
   at org.jpedal.objects.acroforms.rendering.DefaultAcroRenderer.createField(Unknown Source)
   at org.jpedal.objects.acroforms.rendering.DefaultAcroRenderer.createDisplayComponentsForPage(Unknown Source)
   at org.jpedal.PDFtoImageConvertor.convert(Unknown Source)
   at org.jpedal.PdfDecoder.getPageAsImage(Unknown Source)
   at org.jpedal.PdfDecoder.getPageAsImage(Unknown Source)

Here's the location of the plugin, install it into NetBeans IDE 7.2; feedback is very welcome:

http://plugins.netbeans.org/plugin/44525