Split string value in C#

Use:

string s = "REF_SPHCPHJ0000057_Cancel Payer_20100105174151.pdf";
string middleBit = s.Split('_')[2];
Console.WriteLine(middleBit);

The output is

Cancel Payer

This is a place for regular expressions:

Regex re = new Regex(@".*_(?<middle>\w+ \w+)_.*?");
string name = "REF_SPHCPHJ0000057_Cancel Payer_20100105174151.pdf";
string middle = re.Match(name).Groups["middle"].Value;