using System;

using System.Text.RegularExpressions;

​

public class Example

{

    public static void Main()

    {

        string pattern = @"(?<=^\s\S{10})-(?=.*$)";

        string substitution = @" ";

        string input = @" K120613763-01       1100625     TL             -11,008                 0           -11,008                                                                                        

 N123203270-02       1101024     PWL               -387                 0              -387                                                                                        

 I200543078-01       1101029     PDDW              -311                 0              -311                                                                                        

 A122285277-03       1101101     PWL                530                 0               530                                                                                      

 A127477426-03       1101101     PWL                458                 0               458                                                                                      ";

        RegexOptions options = RegexOptions.Multiline | RegexOptions.IgnoreCase;

        Regex regex = new Regex(pattern, options);

        string result = regex.Replace(input, substitution);

        Console.WriteLine(result);

    }

}

​