Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        ' Creamos una lista de archivos para concatenar
        Dim Lista As New List(Of String)
        ' Identificamos los documentos que queremos unir
        Dim sFile1 As String = “C:\Users\Lap\Documents\Visual Studio 2015\Projects\PDF\Cotizacion.pdf”
        Dim sFile2 As String = “C:\Users\Lap\Documents\Visual Studio 2015\Projects\PDF\Cotizacion.pdf”
        ' Los añadimos a la lista
        Lista.Add(sFile1)
        Lista.Add(sFile2)
        ' Nombre del documento resultante
        Dim sFileJoin As String = “C:\Users\Lap\Documents\Visual Studio 2015\Projects\PDF\\DocumentoJoin.pdf”
        Dim Doc As New Document()

        Try
            Dim fs As New FileStream(sFileJoin, FileMode.Create, FileAccess.Write, FileShare.None)
            Dim copy As New PdfCopy(Doc, fs)
            Doc.Open()
            Dim Rd As PdfReader
            Dim n As Integer 'Número de páginas de cada pdf

            For Each file In Lista
                Rd = New PdfReader(file)
                n = Rd.NumberOfPages
                Dim page As Integer = 0
                Do While page < n
                    page += 1
                    copy.AddPage(copy.GetImportedPage(Rd, page))
                Loop
                copy.FreeReader(Rd)
                Rd.Close()
            Next

        Catch ex As Exception
            MsgBox(ex.Message, vbExclamation, “Error uniendo los pdf”)
        Finally
            ' Cerramos el documento
            Doc.Close()
        End Try
    End Sub