File vs Text encryption Rijndael Algorithm

when i used the same code to encrypt a file....i was only able to encrypt the name of the file.....but not the file itself...
so what all changes should i make in my code
nd my code is this...


using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Security.Cryptography;
using System.Web.Security;
using System.Text;
using System.IO;
using System.Data;
using System.Data.SqlClient;

public partial class Default5 : System.Web.UI.Page
{
String sq;
String sq1;
String sq2;
SqlCommand cmd;
SqlCommand cmd1;
SqlCommand cmd2;
SqlConnection cn;
SqlConnection cn1;
SqlConnection cn2;
SqlDataReader sdr;

//ENCRYPTION

private string Encrypt(string plaintext)
{
byte[] rgbIV;
byte[] key;
//byte[] shilpa;

RijndaelManaged rijndael = BuildRigndaelCommon(out rgbIV, out key);

//convert plaintext into a byte array

byte[] plaintextBytes = Encoding.UTF8.GetBytes(plaintext);
//var result = System.Text.Encoding.Unicode.GetBytes(plaintext);
int BlockSize;
BlockSize = 16 * (1 + (plaintext.Length / 16));
Array.Resize(ref plaintextBytes, BlockSize);

// fill the remaining space with 0
for (int i = plaintext.Length; i < BlockSize; i++)
{
plaintextBytes[i] = 0;
}

byte[] cipherTextBytes = null;
//create uninitialized Rijndael encryption obj
using (RijndaelManaged symmetricKey = new RijndaelManaged())
{
//Call SymmetricAlgorithm.CreateEncryptor to create the Encryptor obj
var transform = rijndael.CreateEncryptor();

//Chaining mode
symmetricKey.Mode = CipherMode.CFB;

//create encryptor from the key and the IV value
ICryptoTransform encryptor = symmetricKey.CreateEncryptor(key, rgbIV);

//define memory stream to hold encrypted data
using (MemoryStream ms = new MemoryStream())
{
//define cryptographic stream - contains the transformation key to be used and the mode
using (CryptoStream cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write))
{
//encrypt contents of cryptostream
cs.Write(plaintextBytes, 0, BlockSize);
cs.FlushFinalBlock();

//convert encrypted data from a memory stream into a byte array
cipherTextBytes = ms.ToArray();
}
}
}

//store result as a hex value
string hexOutput = BitConverter.ToString(cipherTextBytes).Replace("-", "");
hexOutput = hexOutput.Substring(0, plaintext.Length * 2);

//finially return encrypted string
return hexOutput;
}





//DECRYPTION

private string Decrypt(string disguisedtext)
{
byte[] disguishedtextBytes = FromHexString(disguisedtext);

var originalLength = disguishedtextBytes.Length;

int BlockSize;
BlockSize = 16 * (1 + (originalLength / 16));
Array.Resize(ref disguishedtextBytes, BlockSize);

// fill the remaining space with 0
for (int i = originalLength; i < BlockSize; i++)
{
disguishedtextBytes[i] = 0;
}


byte[] rgbIV;
byte[] key;

BuildRigndaelCommon(out rgbIV, out key);

string visiabletext = "";
//create uninitialized Rijndael encryption obj
using (var symmetricKey = new RijndaelManaged())
{
//Call SymmetricAlgorithm.CreateEncryptor to create the Encryptor obj
symmetricKey.Mode = CipherMode.CFB;
symmetricKey.BlockSize = 128;
symmetricKey.Padding = PaddingMode.None;

// ICryptoTransform encryptor = symmetricKey.CreateEncryptor(key, rgbIV);