How do I find the classname in C#?

How do you find a programs ClassName? I used:

private void button2_Click(object sender, EventArgs e)
{
string lpClassName = "Notepad";
string lpWindowName = "Untitled - Notepad";
IntPtr hWnd = FindWindow(lpClassName, lpWindowName);
SetForegroundWindow(hWnd);
string z = "TEXT";
const int WM_SETTEXT = 0x0C;
SendMessage(hWnd, WM_SETTEXT, IntPtr.Zero, z);
SendKeys.Send("This is my text");
}

for notepad and it worked just fine, but when I try:

private void button2_Click(object sender, EventArgs e)
{
string lpClassName = "Wordpad";
string lpWindowName = "Document1 - WordPad";
IntPtr hWnd = FindWindow(lpClassName, lpWindowName);
SetForegroundWindow(hWnd);
string z = "TEXT";
const int WM_SETTEXT = 0x0C;
SendMessage(hWnd, WM_SETTEXT, IntPtr.Zero, z);
SendKeys.Send("This is my text");
}

for Wordpad it either just stalls, puts "This is my text" into the textbox in my program, or just puts it in notepad (if it's open). How do I find what the ClassName is?