C# - Merging Two Text Files

using System;

using System.IO;

using System.Linq;

namespace MergeFiles

{

    public class Program

    {

        static void Main(string[] args)

        {

            FileInfo fi = new FileInfo("input");

            fi.MergeFiles("output", "File2", "File3");

        }

    }

    public static class FileInfoExtensions

    {

        public static void MergeFiles(this FileInfo fi,

                                      string strOutputPath,

                                      params string[] filesToMerge)

        {

            var fiLines = File.ReadAllLines(fi.FullName).ToList();

            fiLines.AddRange(filesToMerge.SelectMany(file => File.ReadAllLines(file)));

            File.WriteAllLines(strOutputPath, fiLines.ToArray());

        }

    }

}