Two Approaches for Auto-Starting Windows Applications

1. Startup Folder Shortcut Method (No Admin Rights Required)

This approach creates a shortcut in the Windows startup folder:

using System;
using System.IO;
using IWshRuntimeLibrary;

public class AutoStartManager
{
    private const string AppShortcutName = "MyApplication";
    
    private string StartupPath => 
        Environment.GetFolderPath(Environment.SpecialFolder.Startup);
    
    private string AppPath => 
        System.Diagnostics.Process.GetCurrentProcess().MainModule.FileName;

    public void ConfigureAutoStart(bool enable)
    {
        var existingShortcuts = FindAppShortcuts(StartupPath, AppPath);
        
        if (enable)
        {
            if (existingShortcuts.Count >= 2)
            {
                for (int i = 1; i < existingShortcuts.Count; i++)
                {
                    File.Delete(existingShortcuts[i]);
                }
            }
            else if (existingShortcuts.Count == 0)
            {
                CreateStartupShortcut(StartupPath, AppShortcutName, AppPath);
            }
        }
        else
        {
            foreach (var shortcut in existingShortcuts)
            {
                File.Delete(shortcut);
            }
        }
    }

    private bool CreateStartupShortcut(string folder, string name, string target)
    {
        try
        {
            Directory.CreateDirectory(folder);
            string shortcutPath = Path.Combine(folder, $"{name}.lnk");
            
            var shell = new WshShell();
            IWshShortcut shortcut = (IWshShortcut)shell.CreateShortcut(shortcutPath);
            
            shortcut.TargetPath = target;
            shortcut.WorkingDirectory = Path.GetDirectoryName(target);
            shortcut.Save();
            
            return true;
        }
        catch
        {
            return false;
        }
    }
}

2. Registry Modification Method (Requires Admin Rights)

This approach modifeis the Windows registry:

using Microsoft.Win32;

public class RegistryAutoStart
{
    public static bool SetAutoStart(bool enable)
    {
        string appName = System.Diagnostics.Process.GetCurrentProcess().ProcessName;
        string appPath = System.Diagnostics.Process.GetCurrentProcess().MainModule.FileName;
        return ConfigureRegistry(enable, appName, appPath);
    }

    private static bool ConfigureRegistry(bool enable, string name, string path)
    {
        try
        {
            using (RegistryKey key = Registry.LocalMachine.OpenSubKey(
                @"SOFTWARE\Microsoft\Windows\CurrentVersion\Run", true))
            {
                if (enable)
                {
                    key.SetValue(name, path);
                }
                else
                {
                    key.DeleteValue(name, false);
                }
                return true;
            }
        }
        catch
        {
            return false;
        }
    }
}

Running Application as Administrator

For registry modification, your app needs admin privileges. Here's how to request them:

using System.Security.Principal;
using System.Diagnostics;

static class Program
{
    [STAThread]
    static void Main()
    {
        var identity = WindowsIdentity.GetCurrent();
        var principal = new WindowsPrincipal(identity);
        
        if (principal.IsInRole(WindowsBuiltInRole.Administrator))
        {
            Application.Run(new MainForm());
        }
        else
        {
            var startInfo = new ProcessStartInfo
            {
                FileName = Application.ExecutablePath,
                UseShellExecute = true,
                Verb = "runas"
            };
            
            try
            {
                Process.Start(startInfo);
                Application.Exit();
            }
            catch { }
        }
    }
}

Alternatively, you can modify the application manifest:

<requestedExecutionLevel 
    level="requireAdministrator" 
    uiAccess="false" />