xsl-fo hidden areas within pdf

hi @ll!

i'm new to this list so i'm not aware that someone maybe has asked the
same before (i've had a look at the archive).

my question is:
i want to produce a pdf version of a document from an xml-file which
works fine in general (using apache fop 0.94). i would like to have some
areas visible within the viewing of the pdf file but those areas should
not be printed. is this possible? if yes: could you please provide me
with some details?

thanks in advance
 ...
  werner