C#

private void tbxIntegerEntry_KeyDown(object sender, KeyEventArgs e)
{
    if (e.KeyCode == Keys.Enter)
    {
        string mTxt = tbxIntegerEntry.Text;

        EnteredValue = null;

        // don't evaluate if Text is empty or only minus sign
        if (mTxt != String.Empty && mTxt != "-")
        {
            EnteredValue = Convert.ToInt64(mTxt);
            this.Hide();
        }
    }

    e.SuppressKeyPress =
    !(
        // backspace allowed
        e.KeyCode == Keys.Back
        ||
        // must not exceed length limit
        tbxIntegerEntry.Text.Length <= maxInt64Length
        &&
        // digits allowed
        char.IsDigit(Convert.ToChar(e.KeyCode))
        ||
        // minus sign allowed at position #0
        (tbxIntegerEntry.Text.Length == 0) && (e.KeyCode == Keys.OemMinus)
    );
}

TEXT rt st NEWTEXT 4564

TEXT 4564

Quote:

"FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN 12345 ADDLINE1....."
"FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN # 12345 CITY....."
"FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN: 123 5 COUNTRY....."
"FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN NUMBER ADDLINE1....."

public static Regex regex = new Regex(
      "(PIN\\s?(\\#|:|NUMBER)?\\s?)([\\d\\s]+)",
    RegexOptions.Multiline
    | RegexOptions.CultureInvariant
    | RegexOptions.IgnorePatternWhitespace
    | RegexOptions.Compiled
    );
public static string regexReplace = "$1 ****";
...
   string result = regex.Replace(InputText,regexReplace);

(?<=(PIN|(PIN\s+\#)|(PIN:)|(PIN NUMBER))\s+)\b[\w\s]{2,5}\b

Regex pinNumberPattern = new Regex(@"(?<=(PIN|(PIN\s+\#)|(PIN:)|(PIN NUMBER))\s+)\b[\w\s]{2,5}\b", RegexOptions.ExplicitCapture | RegexOptions.IgnoreCase);

string input = @"FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN 12345 ADDLINE1.....
FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN # 12345 CITY.....
FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN: 123 5 COUNTRY.....
FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN NUMBER ADDLINE1.....";

string output = pinNumberPattern.Replace(input, "*****");

/*
output contains:
FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN ***** ADDLINE1.....
FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN # ***** CITY.....
FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN: ***** COUNTRY.....
FIRSTNAME Tasu LASTNAME Mishra DOB 02011982 PIN NUMBER ADDLINE1.....
*/