How can i password protect my zip file?

i have the code below i got from the net but the problem is no code to protect file the file

Code:
   Public Function CompressFile(ByRef file As String, ByRef destination As String) As String
        'Make sure user provided a valid file with path
        If IO.File.Exists(file) = False Then
            Return "Please specify a valid file (and path) to compress"
            Exit Function
        Else
            'Make sure the destination directory exists
            If IO.Directory.Exists(destination) = False Then
                Return "Please provide a destination location"
                Exit Function
            End If
        End If

        Try
            'Get just the name of the file
            Dim name As String = Path.GetFileName(file)
            'Convert the file to a byte array
            Dim source() As Byte = System.IO.File.ReadAllBytes(file)
            'Now we need to compress the byte array
            Dim compressed() As Byte = ConvertToByteArray(source)
            'Write the new file in the destination directory
            System.IO.File.WriteAllBytes(destination & "\" & name & ".zip", compressed)
           
            Return "Compression Successful!"
        Catch ex As Exception
            Return "Compression Error: " & ex.ToString()
        End Try
    End Function
    Public Function ConvertToByteArray(ByVal source() As Byte) As Byte()
        'Create a MemoryStrea
        Dim memoryStream As New MemoryStream()
        'Create a new GZipStream for holding the file bytes
        Dim gZipStream As New GZipStream(memoryStream, CompressionMode.Compress, True)

        'Write the bytes to the stream
        gZipStream.Write(source, 0, source.Length)
        gZipStream.Dispose()
        memoryStream.Position = 0
        'Create a byte array to act as our buffer
        Dim buffer(memoryStream.Length) As Byte
        'read the stream
        memoryStream.Read(buffer, 0, buffer.Length)
        'CLose & clean up
        memoryStream.Dispose()
        'Return the byte array
        Return buffer
    End Function