How to send a file to asp.net web api with angular?

Basically what i want is to send a file to mi web api and then upload it to azure. this code is triggered when i choose the file, but i'm not sure if it is the correct one.

$scope.fileNameChanged = function(files)
{
    var formD = new FormData();
    var reader = new FileReader();
    reader.onload = function(e)
    {
        $scope.$apply(function()
       {
          $scope.files = reader.result;      
       });
     
    };
    formD.append("file",files.files[0]);
    reader.readAsText(files.files[0]);

    $http({

    method: 'POST',
    headers: {'Content-Type': undefined},
    data:{formD},
    transformRequest : angular.identity,
    url: 'http://localhost:12199/api/FacturacionWeb/PostFormData'
     
    }).success(function(data)
    { 
      
    }).then(function(dat)
      {
        
      })
     
}

<input type="file" multiple onchange="angular.element(this).scope().fileNameChanged(this)">
    <div>Import file...</div>

     <div>
  <textarea ng-model="files" accept=".txt" readonly="true" style="width:99%; height:500px" disabled></textarea>

ASP.NET C# CODE (backend) this code is what i get in the backend but always get "UnsupportedMediaType" i dont know if the problem is with angular or with asp help me please!!

   public async Task<HttpResponseMessage> PostFormData(HttpRequestMessage request)
    {
        // Check if the request contains multipart/form-data.
        if (!Request.Content.IsMimeMultipartContent())
        {
            throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
        }

        string root = HttpContext.Current.Server.MapPath("~/App_Data");
        var provider = new MultipartFormDataStreamProvider(root);

        try
        {
            // Read the form data.
            await Request.Content.ReadAsMultipartAsync(provider);

            // This illustrates how to get the file names.
            foreach (MultipartFileData file in provider.FileData)
            {
                Trace.WriteLine(file.Headers.ContentDisposition.FileName);
                Trace.WriteLine("Server file path: " + file.LocalFileName);
            }
            return Request.CreateResponse(HttpStatusCode.OK);
        }
        catch (System.Exception e)
        {
            return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, e);
        }
    }