I wrote a sample pipeline component for doing that, there is a sample that turns a UBL invoice into a PDF.
You map your Xml file into XSL-FO and then use the pipeline component to convert into PDF. It uses a third party XSL-FO to PDF converter. This sample uses a product from Visual Programming (http://www.xmlpdf.com) but there are a number of other products that could just as easily be used.