Warning: Indexing all PDF Objects when rendering PDF Documents with Angular and ng2-pdf-viewer

Question

My backend creates a PDF based on a formular I submitted. The next page should show the Pdf Documents. I use ng2-pdf-viewer for that purpose. My problem is, that every time I run it the very first time I start my browser I always get the "pdf.worker.min.js:22 Warning: Indexing all PDF objects" warning. When I submit my next formular I dont get the error again and instead it shows the pdf documents.

My GET Request looks as follow:

 this.pdfService.getMaterialPdf().subscribe((file: ArrayBuffer) => {this.pdfMaterial = file});

in the pdfService:

   getMaterialPdf() : Observable<any>
  {
    return this.http.get(this.url+'Material', {responseType:"arraybuffer"});
  }

and the response from the server:

app.get("/pdf/Material", (req, res) => {
      fs.readFile(materialPath,(err, data) => {
        if (err) {
          throw err;
        }
  
        res.send((data));
      });
    });