how can I merge base64 pdf files into one using Laravel?

I have one issue and I would like to know how to fix it.
I have an api that returns base64 pdfs:

{
"resp_1": "JWETRi0xLjMNCiXi48/TDQoNCjEgMCB.....",
"resp_2": "RTGHEgi0xLhjhjjjDQoNCjEgMCB.....",
}

I need to merge them into one file and upload them to S3, for uploading files there is no problem, but the issue here is merging. I am trying this:

...
use Webklex\PDFMerger\Facades\PDFMergerFacade as PDFMerger;
....
.... 

 
   //$resp_1 is JWETRi0xLjMNCiX.....  
   $file_encoded = base64_decode($resp_1);
   $file_encoded_2 = base64_decode($resp_2);

   $oMerger = PDFMerger::init();

    $oMerger->addPDF(mb_convert_encoding($file_encoded, 'UTF-8', 'UTF-8'), 'all');
    $oMerger->addPDF(mb_convert_encoding($file_encoded_2, 'UTF-8', 'UTF-8'), 'all');   
    
    $oMerger->merge();
    $oMerger->save(public_path('storage/merged.pdf'));
.....

> { "message": "Could not locate PDF on '%PDF-1.3\r\n%????......."
> "file": "D:\test\vendor\webklex\laravel-
> pdfmerger\src\PDFMerger\PDFMerger.php", "line": 184, "trace": [
>

What can I do?

Use addString method instead of addPDF (addPDF accept a path to file as an argument):

$oMerger->addString('raw file data', 'all');