Getting data from host, convert to string and then to bytes again.

Hi.
I want to make a program to download files from a remote host.
So what i do is to send throw sockets all the binary information + a string used as end "mystyring".
To check if i have to continue writing the buffer to the file i first convert all to string, so if i find "mystring" it will finish, if not, i reconvert all to bytes and i copy data.
The problem im having is that, .txt files are writed well, but binaris not, it always show error at opening. I ve tried copying a pdf, and when i open it show all the pages, but in blank . Also if i check the size of the original file is always some bytes bigger than the copy.

Code:

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FileStream fs = new FileStream("C:\\Users\\Mauri\\Desktop\\" + item.Name, FileMode.Append, FileAccess.Write);
            BinaryWriter writer = new BinaryWriter(fs);
            bool continua = true;
            while (continua)
            {
                recibido = getSocket(numsock).socketRecv(); // This return the data converted to string.
                words = recibido.Split('|'); //We split "|mystring" to find the end of file.
                foreach (string s in words)
                {
                    if ((String.Compare(s, "mystring") != 0))                       
                        writer.Write(StringToBytes(s)); // Write converted data.
                    else
                        continua = false; // if we find "mystring", end the action.
                } 
            }
            writer.Close();
            fs.Close();

// Convert string to bytes
public byte[] StringToBytes(String cadena)
        {
            System.Text.ASCIIEncoding codificador = new System.Text.ASCIIEncoding();
            return codificador.GetBytes(cadena);
        }

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The strange thing is that .txt files are writed correctly.
I can't use webclient class, beacuse im not downloading the data from an http or ftp server, is for a connection between 2 computers, like a remote access program.

Thanks

i wrote code to download a file from ftp and it worked

Code:

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                string filename_remote = "ftp://......................./file.txt";

                // read file
                WebClient request = new WebClient();
                request.Credentials = new NetworkCredential("username", "password0");
                byte[] buffer = request.DownloadData(filename_remote);

                // get local path
                string dir="C:\\TempDataBase";
                if (!Directory.Exists(dir)) Directory.CreateDirectory(dir);
                string filename_local = Path.GetFileName(filename_remote);
                filename_local = dir + "\\" + filename_local;

                //write to local
                FileStream fs = new FileStream(filename_local, FileMode.Create);
                fs.Write(buffer, 0, buffer.Length);

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I hope it helps..
(ofcoure you should use your own path, username and password)