Export docx to PDF via XSL FO, using FOP
Up until docx4j v3.3.0, this was part of docx4j itself. From 3.3.0 onwards, it is an optional separate sub-project.
In v3.3.0, the default PDF Converter is an eval version of Plutext's commercial renderer, which offers better fidelity and performance.
v6.x series is the last which will support Java 6.