using System;

using System.Web;                   

​

public class Program

{

    public static void Main()

    {

        string fileName = "8dbd4e2_#25001 FINAL-1.jpg";

        // Want to get "8dbd4e2_%2325001 FINAL-1.jpg" or "8dbd4e2_%2325001%20FINAL-1.jpg"

        Console.WriteLine(HttpUtility.UrlEncode(fileName));

        Console.WriteLine(HttpUtility.UrlPathEncode(fileName));

    }

}