Get All Windows Handle

using System.Runtime.InteropServices;

// The signature for the callback method.
public delegate bool CallBack(IntPtr hwnd, int lParam);

[DllImport("user32.dll")]
public static extern int EnumWindows(CallBack callback, int param);
[DllImport("user32.dll")]
public static extern int GetWindowText(IntPtr hWnd,
    StringBuilder lpString, int nMaxCount);

static void Main(string[] args)
{
    // Request that the operating system enumerate all windows,
    // and trigger your callback with the handle of each one.
    EnumWindows(DisplayWindowInfo, 0);
    Console.ReadLine();
}

// The method that will receive the callback. The second
// parameter is not used, but is needed to match the
// callback's signature.
public static bool DisplayWindowInfo(IntPtr hWnd, int lParam)
{
    int chars = 100;
    StringBuilder buf = new StringBuilder(chars);
    if (GetWindowText(hWnd, buf, chars) != 0)
    {
        Console.WriteLine(buf);
    }
    return true;
}