Issue when Uploading PDF files from UI5

Hi Experts,

We have an issue with uploading .PDF attachments via angularjs

Upload works via REST client (postman) as binary data. But not in angularjs.

Angularjs results in a malformed file.

The file is read via file reader (readAsBinaryString).

Code goes like this:

$scope.upload = function($files) {

    if ($files) {

      var r = new FileReader();

      r.onloadend = function(e) {  //end

        var vdata = e.target.result;

        $files[0].binarydata = window.btoa(vdata); //new Uint8Array(r.result);//strTohex(vdata);

        var url = sapUrl+"ZCSMOB_ATTACHMENT_GEN_GW_SRV/FILE_ATTACHMENTSSet";

        $http({method: 'GET', url: url, headers: {'X-CSRF-Token': 'Fetch'}}).then(function(d){

          var token = d.headers('X-CSRF-TOKEN');

          $http({method: 'POST', url: url, headers: {'X-CSRF-Token': token, 'Content-Type': 'application/pdf', 'slug': 'IvBusType~BUS2080#IvFileDesc~Test#IvFileName~Test.PDF#IvIsPicture~X#IvObjKey~002300000281#IvFileType~PDF'}, 'data': $files[0].binarydata}).then(  // , transformRequest: []

            function(d) {

              console.log(d);

            }, function (e) {

              console.log(e);

              //console.log(e.data.error.message.value);

            });

        });

      }

      r.readAsBinaryString($files[0]);

      //r.readAsArrayBuffer($files[0]);

    }

  }

Your Help is very much appreciated.

Thanks.