Tool for Converting from XPS to PDF format

You can install PDF Creator and simply print your XPS file (or any file from any program that has printing capabilities) to PDF.

GhostPDL (sources, binaries), the sibling application to Ghostscript, can do that. It's a commandline tool. Which means you can also script it, and make the conversion non-interactivly. Printing to a "PDF printer" as was suggested above, does work as well of course. But it means you have to open the XPS in a viewer first, then click "print", select the PDF printer, etc. Interactively...

Here is a sample commandline to test the GhostPDL way:

gxps.exe ^
   -o output.pdf ^
   -sPDFSETTINGS=/prepress ^
   input.xps

Another option is to use xpstopdf:

xpstopdf input.xps output.pdf

xpstopdf is part of libgxps, which can be installed by running brew install libgxps in OS X.