using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var fn = "";

        var targetname = @"C:\Users\lashi\Desktop\Klera_Internship (2).lnk";

        var _lfile = @"c:\temp\expt1-log";

        var c = 12; // arbitrary int

​

        // what you're doing now... I don't see you trying to clean any spaces, nor brackets

        fn = targetname.Replace('\\', '_').Replace(":", "_c_");

​

        Console.WriteLine($"Target Before: {targetname}");

        Console.WriteLine($"Destination Before: {_lfile}\\{fn}.{c}");

        fn = targetname.ToSafeFilename();

        Console.WriteLine($"Target After: {targetname}");

        Console.WriteLine($"Destination After: {_lfile}\\{fn}.{c}");

    }

}

public static class StringExtensions{

    public static string ToSafeFilename(this string inString)

    {

        inString = Regex.Replace(inString, @"\\", "_");

        inString = Regex.Replace(inString, @":", "_c_");

        return Regex.Replace(inString, @"[^0-9a-zA-Z_]+", "");

    }

}

​