I have this method to detect the file type:

        ' Return the file type
        ' expC1 File name with the full path
        Public Function FileType(ByVal tcFile As String) As String
            Dim lcString As String = ""
            lcString = FileToStr(tcFile)

            If lcString.Length < 4 Then
                Return ""
            End If

            If Left(lcString, 3) = Chr(255) + Chr(232) + Chr(255) Then
                Return "JPG"
            End If

            If Left(lcString, 3) = "GIF" Then
                Return "GIF"
            End If

            If Mid(lcString, 42, 3) = "EMF" Then
                Return "EMF"
            End If

            If Left(lcString, 4) = Chr(215) + Chr(205) + Chr(198) + Chr(154) Then
                Return "WMF"
            End If

            If Left(lcString, 4) = Chr(77) + Chr(77) + Chr(0) + Chr(42) Then
                Return "TIF"
            End If

            If Left(lcString, 4) = Chr(137) + "PNG" Then
                Return "PNG"
            End If

            If Left(lcString, 2) = "BM" Then
                Return "BMP"
            End If

            If Left(lcString, 3) = "CWS" And Asc(Mid(lcString, 4, 1)) < 16 Then
                Return "SWF"
            End If

            If Left(lcString, 3) = "FWS" And Asc(Mid(lcString, 4, 1)) < 16 Then
                Return "SWF"
            End If

            Return ""
        End Function

    End Class

Now, I need to add file type detection for ZIP, XML, DOC, XLS, PDF and TXT. Is there file detection for some of those I could add?