How Do I Create A File With A Custom Icon Within A Cryptostream?

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C#

WPF

encryption

cryptography

I have a CryptoStream that takes a file and then encrypts said file and outputs a new file with the extension .enc how do i add a icon to this new encrypted file within the CryptoStream method?

This is my CryptoStream method:

using (FileStream inputFileStream = File.Open(inputFile, FileMode.Open))
                   using (FileStream outputFileStream = File.Open(encryptedFile, FileMode.Create))
                   {
                       using (AesCryptoServiceProvider aesCryptoServiceProvider = new AesCryptoServiceProvider())
                       {

                           aesCryptoServiceProvider.BlockSize = 128;
                           aesCryptoServiceProvider.KeySize = 256;
                           aesCryptoServiceProvider.Key = keyBytes;
                           aesCryptoServiceProvider.IV = ivBytes;

                           ICryptoTransform cryptoTransform = aesCryptoServiceProvider.CreateEncryptor();

                           using (CryptoStream cryptoStream = new CryptoStream(outputFileStream, cryptoTransform, CryptoStreamMode.Write))
                           {
                               byte[] buffer = new byte[inputFileStream.Length];
                               inputFileStream.Read(buffer, 0, buffer.Length);
                               cryptoStream.Write(buffer, 0, buffer.Length);
                               MessageBox.Show("The File Was Successfully Encrypted", "Encrypted!", MessageBoxButton.OK, MessageBoxImage.Information);
                           }
                       }
                   }

The path to the icon is set by the user and is displayed in a textbox called OpenIcon.text!

It may not be possible adding a icon to the file in the CryptoStream so if anyone has any other ideas on how one would add an icon to the encrypted file after the CryptoStream?