Form1 f1 = new Form1();

IntPtr intPtr ;
int hwnd = Globals.ThisAddIn.Application.Hwnd;//获取句柄

//intPtr = new IntPtr(hwnd);  //方法一

intPtr = Process.GetCurrentProcess().MainWindowHandle; //方法二

NativeWindow win = NativeWindow.FromHandle(intPtr );
f1.Show(win);

模态关联窗体