Dim bytes() As Byte
 
bytes = IO.File.ReadAllBytes("G:\daten\irgendeine Datei")
Dim str As String = Convert.ToBase64String(bytes, 0, bytes.Length)
 
Dim bytes2() As Byte = Convert.FromBase64String(str)
IO.File.WriteAllBytes("G:\daten\Datei decodiert", bytes2)
 
For i As Integer = 0 To bytes.Length - 1
    If bytes2(i) <> bytes(i) Then Stop
Next i