Maybe I'm wrong but this is a very generic question: how can I cut off a part of a string?
In your case you get a string "1. Name Surname" and need to cut off the leading "1." like e.g. this:
foreach (string sLine in listBox1.SelectedItems)
{
sb.Append(sLine.Replace("1.", "") + Environment.NewLine);
}
Better you use the regular expression - this is very good documented as well, e.g.
Regex.Replace-Methode (String, String)[
^]