I tried using XSL-FO a few years ago and couldn't find a good renderer that
would cope with complex documents. I think things have moved on somewhat and
hopefully in a couple of years the new XSL-FO standard will be implemented
in a commercial component.
I have heard of RenderX but have no first hand knowledge of them.

The usual way is to write an XSLT stylesheet that transforms your XML to
XSL-FO, then you can use a FOP processor to transform the XSL-FO to PDF.
One FOP processor is Apache FOP: http://xmlgraphics.apache.org/fop/

An alternative is to use XSLT to transform to LaTeX, and then process to
PDF. This has the benefit of using LaTeX's built-in foreknowledge of
what documents are, and its large collection of formatting packages,
which avoids you having to reinvent several dozen wheels, and you can
modify your XSLT-->HTML code to output the LaTeX code. LaTeX is
available in both free and commercial implementations, and runs on
almost anything.

Contact me if you need more details.

///Peter

hope this helps...

using System.IO;
using System.Xml.Xsl;
using System.Xml;
using xmlpdf;           //http://www.xmlpdf.com/index.html

namespace xml_to_pdf_example
{
   class Program
   {
       static void Main(string[] args)
       {
           XmlDocument request;
           string stylesheet = "fax.xsl";
           string pdfFile = "yourpdf.pdf";
           XslTransform xsl = new XslTransform();
           xsl.Load(stylesheet);
           MemoryStream pdfXml = new MemoryStream();
           xsl.Transform(request.CreateNavigator(), null, pdfXml, null);
           xmlpdf.licensing.Generator.LicenseFileLocation = "xmlpdf.lic";
           PDFDocument pdfDoc = new PDFDocument();
           MemoryStream pdf = new MemoryStream();
           pdfDoc.generate(pdfXml, pdf);
           FileStream fs = new FileStream(pdfFile, FileMode.OpenOrCreate,
FileAccess.Write, FileShare.None);
           pdf.WriteTo(fs);
           pdf.Flush();
           pdf.Close();
           fs.Close();
       }
   }
}