PDFreactor can be integrated with just these few lines of Java code:

InputSource inputSource = ...; //e.g. new InputSource("http://www.realobjects.com/");
OutputStream outputStream = ...; //e.g. new FileOutputStream("realobjects.pdf");
PDFreactor pdfReactor = new PDFreactor();
pdfReactor.renderDocument(inputSource, new PDFreactorConfiguration(), outputStream);

See also the chapter Introducing the Java lib in the PDFreactor Manual.