The "getting started" document of docx4j contains sample code to write a docx to pdf:
// Set up converter
org.docx4j.convert.out.pdf.PdfConversion c =
new org.docx4j.convert.out.pdf.viaXSLFO.Conversion(wordMLPackage);
However, as of docx4j 3.0, the whole PdfConversion facility seems to be deprecated without a notice how to perform the conversion now. So what is the non-deprecated way of transforming a docx to pdf with the docx4j 3.0.
docx4j 3.0 has a facade you can use to convert to PDF.
There's an example of using it at