OnDoc/API_DocTest/Form3.cs

using Newtonsoft.Json.Linq;
using Syncfusion.Windows.Forms.PdfViewer;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace API_DocTest
{
    public partial class Form3 : Form
    {

        static readonly string ApiUrl = Properties.Settings.Default.DogGenURI;
        static readonly string token = Properties.Settings.Default.Token;
        public Form3()
        {
            InitializeComponent();
        }

        public static byte[] Generate(string json)
        {

            try
            {
                using (var client = new HttpClient())
                {
                    // 🔐 Bearer Token

                    client.DefaultRequestHeaders.Accept.Clear();
                    client.DefaultRequestHeaders.Accept.Add(
                        new MediaTypeWithQualityHeaderValue("application/json"));
                    client.DefaultRequestHeaders.Authorization =
                        new AuthenticationHeaderValue("Bearer", token);

                    var content = new StringContent(
                        json,
                        Encoding.UTF8,
                        "application/json");

                    var response = client.PostAsync(ApiUrl, content).Result;

                    var responseText = response.Content.ReadAsStringAsync().Result;

                    if (!response.IsSuccessStatusCode)
                    {
                        // optional: Logging
                        return null;
                    }

                    var jsonResult = JObject.Parse(responseText);

                    var base64Pdf = jsonResult["file"]?.ToString();

                    if (string.IsNullOrEmpty(base64Pdf))
                        return null;

                    return Convert.FromBase64String(base64Pdf);
                }
            }
            catch (Exception ex)
            {
                // Logging
                return null;
            }
        }
        private void button5_Click(object sender, EventArgs e)
        {
           
            try
            {
              
                byte[] byteArray = Generate(editControl1.Text);
                string temp_inBase64 = Convert.ToBase64String(byteArray);
                var stream = new MemoryStream(Convert.FromBase64String(temp_inBase64));
                if (stream.Length > 0)
                {
                    this.pdfViewerControl1.Load(stream);
                    this.pdfViewerControl1.Visible = true;
                    pdfViewerControl1.ZoomMode = ZoomMode.FitWidth;

                }
                else
                {

                }
            }
            catch (Exception ex) { MessageBox.Show("Fehler beim Generieren." + ex.Message, "Generieren", MessageBoxButtons.OK, MessageBoxIcon.Error); }
        }
    }
}