newbie question - links between two docbooks (pdfs)

["Jan Rudinsky" <jan.rudinsky@strom.cz>]

Hi,
I'd like to know how to create a link between two documents.

I have two docbook.xml files as sources to generate pdf files. How to
add a link from one to the other in docbook so it evolves to a pdf to
pdf link?

Thanks for any suggestions or links :)

JR