The PDF applet download is about 900KB. To open a PDF, select one from this list or open one from the local filesystem, either by using the open icon or by dragging a PDF file from your desktop onto the PDF applet (you will need to trust the PDF applet to do this).
Alternatively, here's a Java Web Start version of the same code. Download (800KB).
If you had Java Web Start installed in your browser, you'd also be able to run the viewer as a Java Web Start application.