Public Sub FindAndMergeFiles(ByVal sourceDir As String)
 
        Const NameCM As String = "CM"
        Const NameGL As String = "GL"
        Const NameImp60 As String = "IMP6000"
        Const NameImp61 As String = "IMP6001"
        Const NameImp62 As String = "IMP6002"
        Const NameImp63 As String = "IMP6003"
 
        Dim curFilename As String
 
        ' Itero cada directorio del directorio de origen.
        For Each topDir As DirectoryInfo In New DirectoryInfo(sourceDir).
                                                GetDirectories("*", SearchOption.TopDirectoryOnly)
 
            ' Itero de forma recursiva cada subdirectorio del directorio actual.
            For Each subDir As DirectoryInfo In topDir.GetDirectories("*", SearchOption.AllDirectories)
 
                ' Itero de forma recursiva cada archivo de texto del directorio actual.
                For Each txtfile As FileInfo In topDir.GetFiles("*.txt", SearchOption.AllDirectories)
 
                    If txtfile.Name.Equals(NameCM, StringComparison.OrdinalIgnoreCase) Then
                        curFilename = NameCM
 
                    ElseIf txtfile.Name.Equals(NameGL, StringComparison.OrdinalIgnoreCase) Then
                        curFilename = NameGL
 
                    ElseIf txtfile.Name.Equals(NameImp60, StringComparison.OrdinalIgnoreCase) Then
                        curFilename = NameImp60
 
                    ElseIf txtfile.Name.Equals(NameImp61, StringComparison.OrdinalIgnoreCase) Then
                        curFilename = NameImp61
 
                    ElseIf txtfile.Name.Equals(NameImp62, StringComparison.OrdinalIgnoreCase) Then
                        curFilename = NameImp62
 
                    ElseIf txtfile.Name.Equals(NameImp63, StringComparison.OrdinalIgnoreCase) Then
                        curFilename = NameImp63
 
                    Else
                        curFilename = String.Empty
 
                    End If
 
                    If Not String.IsNullOrEmpty(curFilename) Then
 
                        Debug.WriteLine(topDir.FullName)
                        Debug.WriteLine(subDir.FullName)
                        Debug.WriteLine(txtfile.FullName)
                        Debug.WriteLine(Path.Combine(topDir.FullName, curFilename))
 
                        Using sr As StreamReader = txtfile.OpenText
                            File.AppendAllText(Path.Combine(topDir.FullName, curFilename), sr.ReadToEnd, Encoding.Default)
                        End Using
 
                    End If
 
                Next txtfile
 
            Next subDir
 
        Next topDir
 
    End Sub

...
' Muevo los directorios (si alguno) con formato de fecha específico (ej. "yyyyMMdd"), del directorio fuente, al directorio de destino.
DateDirUtil.MoveDateDirectories(Me.year, monthNumber, DateDirUtil.DirNameFormat, Me.fdg.SelectedPath, dateDir)
 
' Merge text files.
DateDirUtil.FindAndMergeFiles(Me.fdg.SelectedPath)
...

...
For Each txtfile As FileInfo In topDir.GetFiles("*.txt", SearchOption.AllDirectories)
...

...
Dim enc As Encoding = Encoding.Default
Dim byteData As Byte()
 
Using sr As StreamReader = txtfile.OpenText
 
    Using fs As New FileStream(Path.Combine(topDir.FullName, curFilename),
                               FileMode.Append, FileAccess.Write, FileShare.None, 128)
 
        byteData = enc.GetBytes(sr.ReadToEnd & Environment.NewLine)
        fs.Write(byteData, 0, byteData.Length)
 
    End Using ' fs
 
End Using ' sr
...

Public Sub MergeFiles(ByVal sourceDir As String)
 
    Dim fileNames As String() =
        {
            "CM.txt", "GL.txt",
            "IMP6000.txt", "IMP6001.txt", "IMP6002.txt", "IMP6003.txt"
        }
 
    Dim curFilename As String = String.Empty
 
    For Each topDir As DirectoryInfo In New DirectoryInfo(sourceDir).GetDirectories("*", SearchOption.TopDirectoryOnly)
 
        ' Elimino los archivos principales ("...\topDir\CM.txt", "...\topDir\GL.txt", etc...) de sesiones anteriores.
        For Each txtfile As FileInfo In topDir.GetFiles("*.txt", SearchOption.TopDirectoryOnly)
            If fileNames.Contains(txtfile.Name, StringComparer.OrdinalIgnoreCase) Then
                txtfile.Delete()
            End If
        Next txtfile
 
        For Each subDir As DirectoryInfo In topDir.GetDirectories("*", SearchOption.AllDirectories)
 
            For Each txtfile As FileInfo In subDir.GetFiles("*.txt", SearchOption.AllDirectories)
 
                If fileNames.Contains(txtfile.Name, StringComparer.OrdinalIgnoreCase) Then
 
                    curFilename = fileNames.First(Function(filename) filename.Equals(txtfile.Name, StringComparison.OrdinalIgnoreCase))
 
                    Using sr As StreamReader = txtfile.OpenText
 
                        Using sw As New StreamWriter(Path.Combine(topDir.FullName, curFilename), append:=True, encoding:=Encoding.Default, bufferSize:=128)
                            sw.WriteLine(sr.ReadToEnd)
                        End Using ' sw
 
                    End Using ' sr
 
                End If
 
            Next txtfile
 
        Next subDir
 
    Next topDir
 
End Sub