There are two commonly used tools to generate PDFs from DocBook, dblatex and FOP.

dblatex or FOP?

• dblatex is easier to install, there’s zero configuration required and no Java VM to install — it just works out of the box.
• dblatex source code highlighting and numbering is superb.
• dblatex is easier to use as it converts DocBook directly to PDF whereas before using FOP you have to convert DocBook to XML-FO using DocBook XSL Stylesheets.
• FOP is more feature complete (for example, callouts are processed inside literal layouts) and arguably produces nicer looking output.