Private Shared Function FileFromBase64(ByVal sFileIn As String, 
        sFileOut As String) As Boolean
 
        If Not IO.File.Exists(sFileIn) Then Return False
 
        Try
            Dim str64 As String = IO.File.ReadAllText(sFileIn)
            Dim chars() As Char = str64.ToCharArray
 
            Dim bytes As Byte() = 
              System.Convert.FromBase64CharArray(chars, 0, chars.Length)
 
            Dim stb As New Text.StringBuilder
            For i As Integer = 0 To bytes.Length - 1 Step 1
                stb.Append(ChrW(bytes(i)))
            Next i
 
            IO.File.WriteAllText(sFileOut, stb.ToString)
            Return True
        Catch
            Return False
        End Try
 
End Function

   Dim str64 As String = IO.File.ReadAllText(sFileIn)
 
   Dim bytes() As Byte = System.Convert.FromBase64String(str64)
 
 
   IO.File.WriteAllText(sFileOut, System.Text.Encoding.UTF8.GetString(bytes))