Failed to load PDF document.

this._comms.downLoadCertificate(certificateNumber).subscribe((data) => {
    this.downloadFile(data);
    this.completeLoad();
  }

 downloadFile(response: any) {
  var fileContent = new Blob([response.fileContents], {type:
 'application/pdf' });
  FileSaver.saveAs(fileContent, response.fileDownloadName);
 }

downLoadCertificate(certificateNumber: string) {
let headers = new Headers({
  responseType: ResponseContentType.ArrayBuffer
});
return this._http.get(`${baseUrl}api/UserAdmin/DownloadCertificate/${certificateNumber}`
  , { headers: headers })
  .map(res => res.json())//
  .catch(super.handleError)

[HttpGet]
    [Route("api/UserAdmin/DownloadCertificate/{certificateNumber}")]
    public System.Web.Mvc.FileResult DownloadCertificate(string certificateNumber)
    {
        string path = HttpContext.Current.Server.MapPath("~/Certificates/certificate_#" + certificateNumber + ".pdf");

        System.Web.Mvc.FileContentResult result = new System.Web.Mvc.FileContentResult(File.ReadAllBytes(path), "application/pdf")
        {
            FileDownloadName = certificateNumber + ".pdf"
        };

        return result;

    }