Как сохранить файл pdf в кодировке UTF-8?

require 'vendor/autoload.php'
use PhpOffice\PhpSpreadsheet\Writer\Pdf\Tcpdf;

$spreadsheet = new Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();

$writerPDF = new Tcpdf($spreadsheet);

$writerPDF->writeAllSheets();
$writerPDF->setPreCalculateFormulas(false);
$writerPDF->save($file.'.pdf');