Some problems when embedding external application in winform in C#

Question

I'm trying to embed a external application in a form of winform with c#.It worked well with "nodepad.exe" but my target application using following code.

        Process.Start(@"C:\Program Files\SIMPACK-9.8\run\bin\win64\simpack-viewer.exe");                        
        int timeToWait = 5000;
        while(AppHandle == IntPtr.Zero && timeToWait > 0)
        {
            Thread.Sleep(100);
            timeToWait -= 100;
            foreach (Process pList in Process.GetProcesses())
            {
                if (pList.MainWindowTitle.Contains(@"SIMPACK Viewer"))
                {
                    AppProc = pList;
                    AppHandle = pList.MainWindowHandle;
                    break;
                }
            }
        }


        if (AppHandle != IntPtr.Zero)
        {
            //AppProc.WaitForInputIdle();
            //AppHandle = foreignApp.MainWindowHandle;

            SetParent(AppHandle, this.Handle);
            SetWindowLong(AppHandle, GWL_STYLE, WS_VISIBLE + WS_MAXIMIZE);
            MoveWindow(AppHandle, 0, 0, this.Width, this.Height, true);

        }

My problem is the menu items can't respond to my click but "nodepad" works. Possibly it's because my target application launches through command shell. And I can't apply WaitForInputIdle() function with my target application but notepad can(nodepad need to apply this function actually).

Is anyone can help me, thanks!