How do I compare two files and write a incremental data in another file

using System;
using System.Collections.Generic;
using System.Data;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;

namespace ComparingOfFiles
{
    class Program
    {
        static void Main(string[] args)
        {
            Write("Welcome to file compare program utility, it will generate a file and add some lines, then it will copy it and add more. Finally compare the two and write the added content to a new file.\r\n");

            try
            {
                var parts = Assembly.GetExecutingAssembly().Location.Split(@"\".ToCharArray());
                parts[parts.GetUpperBound(0)] = "";
                var basePath = string.Join(@"\", parts);

                string fileOne = Path.Combine(basePath, "fileone.txt");
                string fileTwo = Path.Combine(basePath, "filetwo.txt");
                string fileResult = Path.Combine(basePath, "fileresult.txt");

                int columns = 8;
                string valuerange = "abcdefghijklmnopqrstuvwxyz";
                string seperator = System.Globalization.CultureInfo.CurrentCulture.TextInfo.ListSeparator;
                var rnd = new Random((int) DateTime.Now.Ticks);
                Write("Deling files if existing");
                foreach(var file in new []{fileOne, fileTwo, fileResult})
                    if(File.Exists(file))
                        File.Delete(file);
                Write("Making log file one");
                using (var fs = new FileStream(fileOne, FileMode.Create))
                {
                    var writer = new StreamWriter(fs, Encoding.UTF8);
                    for (int x = 0; x < 10; x++)
                        AddColumnsOfRandomWords(columns, rnd, valuerange, seperator, writer);
                    writer.Flush();
                    writer.Close();
                }
                Write("Copying to logfile two and adding some lines");
                File.Copy(fileOne, fileTwo);
                using (var fs = new FileStream(fileTwo, FileMode.Append))
                {
                    var writer = new StreamWriter(fs, Encoding.UTF8);
                    for (int x = 0; x < 5; x++)
                        AddColumnsOfRandomWords(columns, rnd, valuerange, seperator, writer);
                    writer.Flush();
                    writer.Close();
                }


                Write("Comparing the two files");
                var sbDifference = new StringBuilder();
                var fileOneContentRows = new List<string>();
                var fileTwoContentRows = new List<string>();

                using (var fs = new FileStream(fileOne, FileMode.Open, FileAccess.Read))
                {
                    var reader = new StreamReader(fs, Encoding.UTF8);
                    while(!reader.EndOfStream)
                        fileOneContentRows.Add(reader.ReadLine());
                    reader.Close();
                }
                using (var fs = new FileStream(fileTwo, FileMode.Open, FileAccess.Read))
                {
                    var reader = new StreamReader(fs, Encoding.UTF8);
                    while (!reader.EndOfStream)
                        fileTwoContentRows.Add(reader.ReadLine());
                    reader.Close();
                }

                using (var fs = new FileStream(fileResult, FileMode.CreateNew))
                {
                    int idx = 1;
                    while (idx < fileOneContentRows.Count())
                    {
                        if (fileOneContentRows[idx].Equals(fileTwoContentRows[idx]))
                        {
                            idx++;
                            continue;
                        }
                        throw new DataException("OMFG! the logs from last weeks have been changed this week!");
                    }
                    if (fileOneContentRows.Count() >= fileTwoContentRows.Count())
                    {
                        sbDifference.AppendLine("Log error, the content of the logfile appears to have decreased between one: " + fileOne + " and two: " + fileTwo);
                    } else
                    {
                        for (int z = idx; z < fileTwoContentRows.Count();z++ )
                        {
                            sbDifference.AppendLine(fileTwoContentRows[z]);
                        }
                    }
                    var writer = new StreamWriter(fs, Encoding.UTF8);
                    writer.Write(sbDifference.ToString());
                    writer.Flush();
                    writer.Close();
                }
                Write("Done");
            } catch (Exception ex)
            {
                Write("Exception occured:\r\n" + ex.ToString());
            }
            Write("\r\nPress ENTER to exit");
            Console.ReadLine();
        }

        private static void AddColumnsOfRandomWords(int columnsToAdd, Random rnd, string valuerange, string seperator, StreamWriter writer)
        {
            for (int i = 0; i < columnsToAdd; i++)
            {
                int length = rnd.Next(1, 20);
                var word = "";
                for (int y = 0; y < length; y++)
                    word += valuerange.Substring(rnd.Next(valuerange.Length - 1), 1);
                if (i < (columnsToAdd - 1))
                    word += seperator;
                writer.Write(word);
            }
            writer.Write("\r\n");
        }

        private static void Write(string message)
        {
            Console.WriteLine(message);
        }
    }
}