The docx4all source code is available from svn - see the immediately preceding forum post.
If that doesn't make any sense to you, maybe you should consider another solution. ... docx4all is java and in particular a Swing application, and the learning curve will be fairly steep if you aren't familiar with the underlying technologies.
You can run it in a web browser via Java Web Start / JNLP.
A different approach would be to convert your docx to HTML, edit it in an HTML editor (eg CKEditor), and then convert the result back to docx.
In contrast, docx4all works natively with the docx format.
Good luck .. Jason