How To Replace As Little As Possible Of The Existing Code

I am receiving the contents of a file via ftp. I don't want to go into every detail (unless needed), but I am working with existing code that was using 3rd-party software to get ftp files. I am replacing that with .NET code. But I want to replace as little as possible of the existing code that is not specifically using the 3rd-party s/w. So I am trying to use a class originally written by the author of the code (a former employee).

This is his class constructor:

Code:

Public Sub New(ByVal fileName As String, ByVal content As StreamReader)
Me.FileName = fileName
Me.Content = content
Me.TimeStamp = Date.Now
End Sub

So I need to pass a StreamReader. My problem is how to get one.
In my procedure ReceiveFile(), I execute this code:

Code:

Private Shared Sub ReceiveFile(ByVal sFilename As String, ByRef objMemoryStream As System.IO.MemoryStream)
Try

Dim request As FtpWebRequest = DirectCast(WebRequest.Create("ftp site and folder" & sFilename), FtpWebRequest)
request.Method = WebRequestMethods.Ftp.DownloadFile
request.Credentials = New NetworkCredential("id", "pw")
Dim response As FtpWebResponse = DirectCast(request.GetResponse(), FtpWebResponse)
Dim responseStream As Stream = response.GetResponseStream()
Dim reader As New StreamReader(responseStream)
Dim sFile As String = reader.ReadToEnd
'reader.Close()
' response.Close()
'objMemoryStream = responseStream
Dim objStream As System.IO.MemoryStream
objStream = New System.IO.MemoryStream(Convert.FromBase64String(sFile))
' objMemoryStream = Convert.FromBase64String(sFile)
objMemoryStream = objStream
'Return reader
Catch ex As Exception
Dim i As Integer
i = 10
End Try
End Sub

responseStream is declared as a stream but when I query it in the debugger it says it's an FtpDataStream, after it's set equal to response.GetResponseStream. I want to take that stream and somehow get it into a MemoryStream. I thought I found the solution this morning via Convert.FromBase64String, but when I ran I got an exception saying "Invalid character in a base-64 string", and I think it's because of the newline character in the string. The file that's received contains three lines separated by a newline character.