use strict;
use PDF::API2;

my $pdf = PDF::API2->new( -file => "path/to/outfile.pdf" );
my @files = glob ("path/to/somewhere/else/*.pdf");
merge (@files);

# some stuff

sub merge
{
    my 
    (
        $file,
        $root,
    );

    $root = $pdf->outlines;

    my $import_page = 0;
    my $document_page = 0;

    foreach $file ( @_ )
    {
        my ($inputpdf, $inputdir) = fileparse ($file);       

        my $input = PDF::API2->open( $file );

        my @pages = 1 .. $input->pages;

        if ( scalar @pages > 0 ) 
        {
            my $outline;

            $outline = $root->outline
                if $bookmark;

            foreach ( @pages ) 
            {
                ++$import_page;
                ++$document_page;

                my $page = $pdf->importpage($input, $_, $import_page);

                if ( $bookmark )
                {
                    my ($bmtext) = ($inputpdf =~ /([^\.]+)/ );
                    $outline->title($bmtext);

                    my $bm = $outline->outline;
                    $bm->title("Seite $document_page");

                    $bm->dest($page);
                    $outline->dest($page) if $document_page == 1;
                    $outline->closed;
                }
            }

        }
    }
    
    $pdf->preferences( -outlines => 1 )
        if $bookmark;

    $pdf->update;
    $pdf->end;
}