For simple XML, PDF generation is built into Splunk 5.X (and I must admit : is not bug-free...)
For either:
Advanced XML
Simple XML with forms
Advanced XML with forms
You have to use the PDF report server. Installing this app is not very trivial but since I've done it, I've noticed there is a new release. Most of the problems I remember were linked to undocumented missing dependancies, but basically, if you install "firefox" on your PDF server, you should pull out all the necessary packages and libraries.
Although it is said it's only supported with 4.X, I also had to install the following app (and fix it, as written in the comments at the end of the page). It may not be necessary anymore with the new PDF report server :
http://splunk-base.splunk.com/apps/26915/pdf-download-extension-42-only
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