I think you are looking for PDF::API2. The pod mentions explicitly:

    $pdf->info(
        'Author'       => " Alfred Reibenschuh ",
        'CreationDate' => "D:20020911000000+01'00'",
        'ModDate'      => "D:YYYYMMDDhhmmssOHH'mm'",
        'Creator'      => "fredos-script.pl",
        'Producer'     => "PDF::API2",
        'Title'        => "some Publication",
        'Subject'      => "perl ?",
        'Keywords'     => "all good things are pdf"
    );
[download]

and

    $pdf->update

    Updates a previously "opened" document after all changes 
    have been applied.
[download]

This looks like what you want ...