It must be a problem with that particular AZW4 file (or your python installation), because I have no difficulties extracting the PDFs from AZW files using the latest mobi_unpack (v.50). It's interesting that it appears to be the console-less pythonw interpreter that's actually doing the crashing. Have you tried bypassing the GUI front-end for mobiunpack and just running it from the command prompt? That would take pythonw.exe out of the equation.
Also, you could try the
third-party calibre plugin version of MobiUnpack. It will allow you to extract the PDF from the AZW4 file (with no conversion involved). You can use calibre's built-in "Get new plugins" functionality to automatically install the plugin.