Basically, it require an Stylesheet to convert XML to PDF.
If your XML already comply with built-in Doctypes such as DITA, there are already stylesheets come with Arbortext Editor. You can use a print compose license in Arbortext Editor or Publish Engine to convert XML to PDF using the stylesheet.
If your XML comply with customized Doctype, you will need a stylesheet for it. In Arbortext, you can create stylesheet using 1) Styler. 2) XSLT/XSL-FO.3)FOSI.
Extra license for print compose and Publish Engine required.
Hope this helps