Angular ng-file-upload - What is ngfBlobUrl and how to convert back and forth

Question

I am looking into allowing users to upload PDF files (and later preview/download them back). I was looking around and it seems that ng-File-Upload is a popular directive to upload files since it supports many browsers.

I originally thought that I would have to convert my PDF's to blobs and store them in my SQL database and then convert back to PDF when given them the option to preview/download.

Playing around with ng-file-upload I see that when one uploads a file in the manner (taken from their sample page):

  $scope.uploadFiles = function (file, errFiles) {
    console.log(file);

    $scope.f = file;
    $scope.errFile = errFiles && errFiles[0];
    if (file) {
        file.upload = Upload.upload({
            url: 'https://angular-file-upload-cors-srv.appspot.com/upload',
            data: { file: file }
        });

        file.upload.then(function (response) {
            $timeout(function () {
                file.result = response.data;
            });
        }, function (response) {
            if (response.status > 0)
                $scope.errorMsg = response.status + ': ' + response.data;
        }, function (evt) {
            file.progress = Math.min(100, parseInt(100.0 *
                                     evt.loaded / evt.total));
        });
    }
  }
}]);

and me checking out the file properties in the console I see a property called $ngfBlobUrl:

$ngfBlobUrl: "blob:http%3A//localhost%3A54170/0cc4b67a-9f6a-4833-acd0-7fd51e00996e

I am curious if anyone can give me any insight on how they generate this I assume in the file upload and if this is exactly what I need for my solution and if so can anyone point me to documentation on how I would go about converting it back to its original PDF form. I am trying to understand more how ng-file-upload works and whether it is a viable directive for my project or not.

Thanks