Hi,
We have a DITA OT plugin which customizes the output for our Oxygen user's manual. It's available for free on GitHub:
https://github.com/oxygenxml/com.oxygenxml.pdf2.ugand it also has some header and footer customizations, maybe you could use it as an example:
https://github.com/oxygenxml/com.oxygenxml.pdf2.ug/wikiThere is also a book called "DITA For Print":
http://xmlpress.net/publications/dita/dita-for-print/which should cover lots of PDF customization scenarios.
About your second question:
Can I use the key in the footer, which is defined in the map?
Sometimes people use in the DITA Map various DITA <data> elements with custom names, and then in the PDF XSLT customization they can match on those particular <data> elements and extract values from them.
For questions which are not Oxygen specific you can also register and ask on the DITA Users List:
https://groups.yahoo.com/neo/groups/dita-users/infoIt's a large community of DITA experts and they can also help with customization questions.
Regards,
Radu