No. That can't work. That's also not what I showed. You will need to supply that parameter yourself, outside of the "parameters". A subroutine reference never takes parameters. Maybe something like the following:

my $pdf = PDF::API2::Simple->new( 
    header => \&my_header($CategoryName),
    footer => \&footer,
    margin_left => 15,
    margin_top => 15,
    margin_right => 15,
    margin_bottom => 45
);

sub my_header
{
    my $pdf = shift;
    my $cat = $CategoryName;
    
    print $cat;
    
    header($pdf);
}

sub header {
  my $pdf = shift;
  # do my stuff
}
[download]

... or, alternatively, if your $CategoryName changes several times before your (different) PDF objects output themselves, you can create the subroutines anonymously on the fly:

my $pdf = PDF::API2::Simple->new( 
    header => sub {
            my_header($CategoryName),
        },
    footer => \&footer,
    margin_left => 15,
    margin_top => 15,
    margin_right => 15,
    margin_bottom => 45
);

sub header {
  my $pdf = shift;
  # do my stuff
}
[download]

Thanks, Corion! I tried your suggestions. The first one can't work because the category name is changes in a loop I make after defining the pdf object. The second one gave the same 'not a code reference...' error. I placed a variable outside the fuctions which I set in my first function and use in the header function. Thanks you very much!