var uri = "https://westeurope.api.cognitive.microsoft.com/vision/v2.0/recognizeText?mode=Printed";


            var client = new HttpClient();
            var httpRequestMessage = new HttpRequestMessage
            {
                 Method = HttpMethod.Post,
            RequestUri = new Uri(url),
            Headers = {
                {"Ocp-Apim-Subscription-Key", "06643f25ad804b869f9298b37a6b4793" },
                { HttpRequestHeader.ContentType.ToString(), "application/octet-stream" },
            },
            Content = fileStream
            };

            var response = await client.SendAsync(httpRequestMessage);
            response.Content; //wyciągasz z contentu "Operation-Location" - jest to adres, po który dalej strzelamy

            var requestUri = wyciagnieteOperationlocation;

            using(var requestMesssage = new HttpRequestMessage(HttpMethod.Get, requestUrl))
            {
              requestMesssage.Headers.Add("Ocp-Apim-Subscription-Key", "06643f25ad804b869f9298b37a6b4793");
              var respRequest = await client.SendAsync(requestMesssage);

              return new List<string>{(await respRequest.Content.ReadAsStringAsync())};
            }