Rotate existing pdf file's first page to 90 degrees using perl script

I want to rotate only first page of all existing pdfs present in a directory to 90 degrees using perl script.

I am using below script for rotation, but not working in my case.

Note: I am not getting any compilation issues.

use strict;
use PDF::API2;     #using PDF::API2 => 2.039 version 
use PDF::API2::Page;

opendir(DIR,$dirname) or die;
my output_file = 'new.pdf';
my output_pdf = PDF::API2->new(-file => $output_file);

while(my $file_name = readdir(DIR)){
 my $input_pdf = PDF::API2->open($file_name);
 my @numpages = (1..$input_pdf->pages());

 foreach my $pagnum (@numpages){
   if($pagnum==1){
     my $page = $input_pdf->openpage($pagnum);
     $page = $page -> rotate(90); 
   }
   $output_pdf->importpage($input_pdf,$pagnum,0);
 }

}
$output_pdf.save();
closedir(DIR);