C#

private void button1_Click(object sender, EventArgs e) 
{
    Process p = Process.Start("Notepad.exe");
    p.WaitForInputIdle(); 
    SetParent(p.MainWindowHandle, panel1.Handle);
    SetWindowPos(
        p.MainWindowHandle,
        IntPtr.Zero,
        0, 0,
        panel1.Width, panel1.Height,
        0u);
}
[DllImport("user32.dll", EntryPoint = "SetParent", SetLastError = true)]
private static extern IntPtr SetParent(IntPtr hwndChild, IntPtr hwndParent);

[DllImport("user32.dll")]
private static extern bool SetWindowPos(
    IntPtr hWnd,
    IntPtr hWndInsertAfter,
    int X, int Y,
    int cx, int cy,
    uint uFlags);

DaveyM69 wrote:

The problem was Notepad remembers it's last size and location and it assumes that relative to the hwnd's top left.

drago123 wrote:

How can I add a button when run time?

Button b = new Button();
this.Controls.Add(b);

drago123 wrote:

and if there is a button in the form, how can it added next to it? Could you help me,please?

// Set the left position to be the same as the existing button.
int left = existingButton.Left;
// Plus the width of the existing button.
left += existingButton.Width;
// Plus a small gap.
left += 20;

// Set the top of the new button to be the same as the existing button.
int top = existingButton.Top;

// Create the new button.
Button newButton = new Button();

// Assign the left & top values to position the button.
newButton.Left = left;
newButton.Top = top;

// Add the new button to the controls collection.
this.Controls.Add(newButton);