I was looking for a way to convert swagger2markup markdown output to docx using Java (as opposed to Pandoc).

I found flexmark-java which describes itself as:

Java Markdown parser with source level AST. CommonMark 0.28, emulation of: pegdown, kramdown, markdown.pl, MultiMarkdown. With HTML to MD, MD to PDF, MD to DOCX conversion modules.

Its MD to DOCX is in flexmark-docx-converter module, which happily, uses docx4j under the covers.

I tried it, and found it works nicely, the exception being table rendering if you open the resulting docx in LibreOffice (Word automatically sets the column widths, but in LibreOffice 5.3 Writer, the column widths are bad and painful to fix).   The underlying issue is that markdown doesn’t specify column widths, and in docx4j, we don’t provide an algorithm to help the user set sensible values.

Development of flexmark-docx-converter was  sponsored by Johner Institut GmbH (medical device documentation)

The documentation for flexmark-docx-converter is at https://github.com/vsch/flexmark-java/wiki/Docx-Renderer-Extension

That page says:

Word does not handle inserted HTML very well.

It would be quite straightforward to use docx4j-ImportHTML to work around that