This method enables you to select all text within the control.
public void CopyAllMyText()
{
// Determine if any text is selected in the TextBox control.
if(textBox1.SelectionLength == 0)
// Select all text in the text box.
textBox1.SelectAll();
// Copy the contents of the control to the Clipboard.
textBox1.Copy();
}
Check this link for more info. http://msdn.microsoft.com/en-us/library/system.windows.forms.textboxbase.selectall.aspx