از این کد استفاده کنید :
private void textBox2_KeyDown(object sender, KeyEventArgs e)
{
int SelectedIndex = textBox2.SelectionStart;
if (e.KeyCode == Keys.Space)
{
string[] strWord = textBox2.Text.Split(' ');
if (strWord.Length > 0)
{
for (int i = 0; i < strWord.Length; i++)
strWord[i] = strWord[i].Substring(0, 1).ToUpper() + strWord[i].Substring(1);
}
textBox2.Text = "";
for (int i = 0; i < strWord.Length; i++)
{
textBox2.Text += strWord[i] + " ";
}
textBox2.Text = textBox2.Text.Substring(0, textBox2.Text.Length - 1);
textBox2.SelectionStart = SelectedIndex;
}
}