Here is an example which uses WWW::Mechanize to visit the page, populate the field and submit the form. Error checking is left as a exercise for you, this is a short example to get you started:
my $url = 'http://www.kultusportal-bw.de/servlet/PB/menu/1188427_pfhan
my $mech = WWW::Mechanize->new();
$mech->get( $url );
# $mech->content now contains the results page.
I can't read German, so you'd better check that you're not breaking any site policy regarding automation.