OnDoc/API_DocTest/Form2.cs

using Newtonsoft.Json.Linq;
using Syncfusion.Windows.Forms.PdfViewer;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
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.Web.UI.Design;
using System.Windows.Forms;

namespace API_DocTest
{
    public partial class Form2 : Form
    {
        static string connectionstring = Properties.Settings.Default.ConnectionString;
        static readonly string ApiUrl = Properties.Settings.Default.DogGenURI;
        static readonly string token = Properties.Settings.Default.Token;
        private string path = Properties.Settings.Default.PathUser.Replace("[userid]", Environment.UserName);

        public Form2()
        {
            InitializeComponent();
        }

        private void Form2_Load(object sender, EventArgs e)
        {
             string lickey = "MzYzODg2NkAzMjM4MmUzMDJlMzBTOWljRmxNelA1d1VGOHpGR0lxQzB6UTAwKzIxK2VBNEhBZFp5alcxb1NVPQ==";
            Syncfusion.Licensing.SyncfusionLicenseProvider.RegisterLicense(lickey);
            if (!System.IO.Directory.Exists(path)) { System.IO.Directory.CreateDirectory(path); }
            label1.Text = "JSON-Pfad: " + path;
            Refresh_Filelist();

        }

        private void Refresh_Filelist()
        {
            listBox1.Items.Clear();
            DirectoryInfo d = new DirectoryInfo(path); //Assuming Test is your Folder

            FileInfo[] Files = d.GetFiles("*.json"); //Getting Text files
            string str = "";

            foreach (FileInfo file in Files)
            {
                listBox1.Items.Add(file.Name);
            }

        }

        private void button3_Click(object sender, EventArgs e)
        {
            if (radioButton1.Checked) { connectionstring = Properties.Settings.Default.ConnectionString; }
            if (radioButton2.Checked) { connectionstring = Properties.Settings.Default.ConnectionStringPrd; }
            string key = txtfilekey.Text.Trim();
            if (key == "") { MessageBox.Show("ESS_Key fehlt");return; }

            string json = null;
            using (SqlConnection con = new SqlConnection(connectionstring))
            using (SqlCommand cmd = new SqlCommand(
                "SELECT JavaScriptObject FROM ProvDokuments WHERE ProvDokumentid = @key", con))
            {
                cmd.Parameters.AddWithValue("@key", key);
                con.Open();
                json = cmd.ExecuteScalar()?.ToString();
            }
            if (string.IsNullOrEmpty(json)) { MessageBox.Show("Eintrag mit dem Schlüssel '" + txtfilekey.Text + "' ist nicht vorhanden.","Laden",MessageBoxButtons.OK,MessageBoxIcon.Error);return; }
            if (string.IsNullOrEmpty(txtfilename.Text.Trim()) || txtfilename.Text=="") { txtfilename.Text=txtfilekey.Text; }
            System.IO.File.WriteAllText(path + txtfilename.Text + ".json", json);
            
            Refresh_Filelist();
            foreach(string s in listBox1.Items)
            {
                if (s == txtfilename.Text+".json") { listBox1.SelectedItem = s;
                    txtfilekey.Text = "";
                    txtfilename.Text = "";

                    return; }
            }
            txtfilekey.Text = "";
            txtfilename.Text = "";
        }

        private void button5_Click(object sender, EventArgs e)
        {
            try
            {
                string filename = path + listBox1.SelectedItem.ToString();
                byte[] byteArray = Generate(System.IO.File.ReadAllText(filename));
                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); }
        }

        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 button1_Click(object sender, EventArgs e)
        {
            try
            {
                if (File.Exists(path + listBox1.SelectedItem.ToString()))
                {
                    System.IO.File.Delete(path + listBox1.SelectedItem.ToString());
                    Refresh_Filelist();
                }
            }
            catch(Exception ex)
            {
                MessageBox.Show("Beim Löschen ist ein Fehler aufgetreten:" + ex.Message, "Löschen", MessageBoxButtons.OK, MessageBoxIcon.Error); 
            }
        }
    }
}