Licensing information is not populated into PDFs from the Download as PDF left nav link, or from Book Creator. I've confirmed that I have correctly set the license variables:
$wgLicenseName = "Creative Commons Attribution-Share Alike 3.0 license";
$wgLicenseURL = "http://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_License";
I also set both variables to null as a test to see if the RightsText and RightsUrl variables would default, but they did not.