How should it be done to move Focus from Trados to plugin Form certainly?

Hello,
I am making "Right Click plus for Three D Menu", which separates " right click of a mouse" and "Ctrl+ right click of a mouse", now.
Now,this can indicate Three D Menu Form by "Ctrl + right click" and operate normally by "right click" only.
But focus still stays in Trados at the time of Form indication.
How should it be done to move Focus from Trados to Form certainly?

(When making them indicate by "Ctrl+5", a focus normally moves to Form from Trados.)
 
//a part of Three D Menu program
        private void Form1_Shown(object sender, EventArgs e)
        {
            System.Threading.Thread.Sleep(100);
            this.Activate();           
            this.Focus();
        }