Format conversion between PDF and DocBook

I have been searching around but so far
I had no direct answers.

Normally what we have is from FO to PDF direction only.
There is no direct conversion between PDF and DocBook.

Indeed, PDF is not an XML file so, I guess,
hardly I will find and XSLs that make the
conversion between PDF and DocBook.

Could anyone tell me where I should look besides the Apache site?

My intention is to write Servlets that make the calls to API
and outpus either PDF or DocBook depending on the request.
Which XSL are available and
where to get DocBook-FO converter?

Any help is appreciated.
Carlos




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