Вы можете сделать это следующим образом:
[DllImport("user32.dll")]
static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);
[DllImport("user32.dll")]
static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);
[DllImport("user32.dll", SetLastError = true)]
private static extern bool MoveWindow(IntPtr hwnd, int x, int y, int cx, int cy, bool repaint);
[DllImport("user32.dll", SetLastError = true)]
static extern void SwitchToThisWindow(IntPtr hWnd, bool fAltTab);
[DllImport("user32.dll")]
static extern IntPtr SetActiveWindow(IntPtr hWnd);
private const int GWL_STYLE = (-16);
private const int WS_VISIBLE = 0x10000000;
private const int WS_MAXIMIZE = 0x01000000;
private void Form1_Load(object sender, EventArgs e)
{
this.SuspendLayout();
Process notepad = new Process();
ProcessStartInfo psi = new ProcessStartInfo("notepad.exe");
psi.WindowStyle = ProcessWindowStyle.Normal;
notepad.StartInfo = psi;
notepad.Start();
this.ResumeLayout();
notepad.WaitForInputIdle(3000);
IntPtr old = SetParent(notepad.MainWindowHandle, this.Handle);
SetWindowLong(notepad.MainWindowHandle, GWL_STYLE, WS_VISIBLE + WS_MAXIMIZE);
MoveWindow(notepad.MainWindowHandle, 100, 100, 400, 400, true);
SetActiveWindow(notepad.MainWindowHandle);
SwitchToThisWindow(notepad.MainWindowHandle, true); }
Таким образом, у вас есть приложение Notepad в вашей форме;)