encryption error

Hello, I am using laravel DOMpdf to create a pdf file. I also want to merge pdf files of database into DOMpdf file. Please could anyone let me know , how to check a file is encrypted or not. I think bocause of an encrypted pdf file I am getting enryption error , when creating pdf.

$merger = new \PDFMerger;

foreach($workerCertificates as $certificates) {

$merger->addPDF(public_path().urldecode($certificates['url']));

}

return $merger->merge('stream', "package-$item->number.pdf");

thanx