private void button1_Click(object sender, EventArgs e)
for (int i = 0; i < Application.OpenForms.Count; i++)
If you wish to have it maximised for only few types of forms, you can put if condition in that for loop.
These lines will make all openforms in your application maximised :)
Also for panel1,
Add line of code,
Let me know if you need any more help..