Private Sub Button397_Click_1(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button397.Click
        With New MergePDFs.Form10
            .Show()
        End With
End Sub

Imports iTextSharp.text
Imports iTextSharp
Imports iTextSharp.text.pdf
 
Public Class cMergePDF
 
  Public Function MergePdfFiles(ByVal pdfFiles() As String, ByVal outputPath As _
    String) As Boolean
    Dim result As Boolean = False
    Dim pdfCount As Integer = 0 'total input pdf file count
    Dim f As Integer = 0 'pointer to current input pdf file
    Dim fileName As String = String.Empty 'current input pdf filename
    Dim reader As iTextSharp.text.pdf.PdfReader = Nothing
    Dim pageCount As Integer = 0 'cureent input pdf page count
    Dim pdfDoc As iTextSharp.text.Document = Nothing 'the output pdf document
    Dim writer As PdfWriter = Nothing
    Dim cb As PdfContentByte = Nothing
    Dim page As PdfImportedPage = Nothing
    Dim rotation As Integer = 0
    Try
      pdfCount = pdfFiles.Length
            If pdfCount > 0 Then
                fileName = pdfFiles(f)
                reader = New iTextSharp.text.pdf.PdfReader(fileName)
                pageCount = reader.NumberOfPages
                pdfDoc = New iTextSharp.text.Document( _
                  reader.GetPageSizeWithRotation(1), 18, 18, 18, 18)
                writer = PdfWriter.GetInstance(pdfDoc, New IO.FileStream( _
                outputPath, IO.FileMode.Create))
                With pdfDoc
                    .AddAuthor("blas")
                    .AddCreationDate()
                    .AddCreator("")
                    .AddSubject("Zusammenführung von PDF-Dokumenten")
                    .AddTitle(IO.Path.GetFileNameWithoutExtension(outputPath))
                    .AddKeywords("Report, Merged PDF, " & IO.Path.GetFileName( _
                      outputPath))
                    .Open()
                End With
                cb = writer.DirectContent
                While f < pdfCount
                    Dim i As Integer = 0
                    While i < pageCount
                        i += 1
                        pdfDoc.SetPageSize(reader.GetPageSizeWithRotation(i))
                        pdfDoc.NewPage()
                        page = writer.GetImportedPage(reader, i)
                        rotation = reader.GetPageRotation(i)
                        If rotation = 90 Then
                            cb.AddTemplate(page, 0, -1.0F, 1.0F, 0, 0, _
                              reader.GetPageSizeWithRotation(i).Height)
                        ElseIf rotation = 270 Then
                            cb.AddTemplate(page, 0, 1.0F, -1.0F, 0, _
                              reader.GetPageSizeWithRotation(i).Width + 60, -30)
                        Else
                            cb.AddTemplate(page, 1.0F, 0, 0, 1.0F, 0, 0)
                        End If
                    End While
                    f += 1
                    If f < pdfCount Then
                        fileName = pdfFiles(f)
                        reader = New iTextSharp.text.pdf.PdfReader(fileName)
                        pageCount = reader.NumberOfPages
                    End If
                End While
                pdfDoc.Close()
                result = True
            End If
    Catch ex As Exception
      MessageBox.Show("Fehler beim Mergen - " & ex.Message)
    End Try
    Return result
  End Function
 
End Class

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button3.Click
 
        Dim oMerge As New cMergePDF
        Dim Fils As New ArrayList
        Dim strFiles() As String
 
            For idx As Integer = 0 To Fils.Count - 1
                ReDim Preserve strFiles(idx)
                strFiles(idx) = Fils(idx)
                oMerge.MergePdfFiles(strFiles, ausgabedatei)
            Next
 
        Me.Close()
 
    End Sub