PDF Layer Merger

 

Recently I’ve created a simple .NET tool, to merge 2 PDF files, one as a layer on top of the other.

The reason behind this, was to be able to digitally remark/comment/mark-up on a PDF file using AutoCAD.  People tend to print out a PDF file, use some highlighters and draw some clouds and comments on this PDF, only to re-scan this afterwards.
This is the way we used to work, but today we live in a digital era…

The tool has been built in VB.NET targeting the NET 2.0 framework, with the use of the excellent PDF library iTextSharp (based on iText).

Snippet of the actual transformation function:

  
    ''' 

    ''' Combines two source pdf's to one single pdf.
    ''' 
    ''' The file-location incl. the name of the original pdf.
    ''' The file-location incl. the name of the mark-up pdf.
    ''' The file-location incl. the name of the generated combined pdf.
    ''' The name which the added mark-up layer will have in the new pdf.
    ''' The transformation which is executed on the original pdf: rotation, scaleX, scaleY, offsetX, offsetY
    ''' Return boolean indication whether the combination of the pdf's was successful.
    ''' 
    Public Function PDFCombineLayer(ByVal sourceOriginal As String, ByVal sourceMarkup As String, ByVal destination As String, Optional ByVal NewLayer As String = "SOURCE-DRAWING", Optional ByVal Transform As String = "0;1;1;0;0") As Boolean
        Dim oPdfOriginal As iTextSharp.text.pdf.PdfReader = Nothing
        Dim oPdfMarkup As iTextSharp.text.pdf.PdfReader = Nothing
        Dim oPdfStamper As iTextSharp.text.pdf.PdfStamper = Nothing
        Dim PDFDirectContent As iTextSharp.text.pdf.PdfContentByte
        Dim iNumberOfPages As Integer = Nothing
        Dim iPage As Integer = 0
        Dim matrix1 As Drawing2D.Matrix = Nothing
        Dim matrix2 As Drawing2D.Matrix = Nothing

        Try
            'Read the source pdf-files and prepare new file.
            oPdfOriginal = New iTextSharp.text.pdf.PdfReader(sourceOriginal)
            oPdfMarkup = New iTextSharp.text.pdf.PdfReader(sourceMarkup)
            oPdfStamper = New iTextSharp.text.pdf.PdfStamper(oPdfMarkup, New IO.FileStream(destination, IO.FileMode.Create, IO.FileAccess.Write))

            'Count pages in original pdf and create new pdf wih same amount of pages.
            iNumberOfPages = oPdfOriginal.NumberOfPages
            oPdfStamper.GetPdfLayers()

            'Make transformation matrix
            If Transform = "" Then Transform = "0;1;1;0;0" 'Note transform: rotation(degrees), scaleX, scaleY, offsetX, offsetY
            Dim ar() As String = Split(Transform, ";")
            If Not ar.Length = 5 Then ar = New String() {0, 1, 1, 0, 0}
            If ar(1) <= 0 Or ar(2) <= 0 Then Throw New ArgumentOutOfRangeException("transform", "Make sure that scaling factors of the transformation are larger than zero.")
            matrix1 = New Drawing2D.Matrix
            matrix1.Rotate(-CSng(ar(0)))
            matrix1.Scale(CSng(ar(1)), CSng(ar(2)))
            matrix1.Translate(CSng(ar(3)), CSng(ar(4)))
            matrix2 = New Drawing2D.Matrix

            'Add the new layer to each of the pdf-pages.
            If NewLayer = "" Then NewLayer = "SOURCE-DRAWING"
            Dim PDFNewLayer As New iTextSharp.text.pdf.PdfLayer(NewLayer, oPdfStamper.Writer)
            Dim PDFLayerMem As New iTextSharp.text.pdf.PdfLayerMembership(oPdfStamper.Writer)
            PDFLayerMem.AddMember(PDFNewLayer)
            Do While (iPage < iNumberOfPages)
                'Get new page
                iPage += 1
                Dim iPageOriginal As iTextSharp.text.pdf.PdfImportedPage = oPdfStamper.Writer.GetImportedPage(oPdfOriginal, iPage)
                PDFDirectContent = oPdfStamper.GetUnderContent(iPage) 'add page under existing pdf in new layer
                matrix2 = matrix1.Clone 'Cloning is necessary, otherwise all adaptations to matrix2 are also done in matrix1.

                'Compensate for the orientation of the original pdf-file.
                Dim iRotation As Single = oPdfOriginal.GetPageRotation(iPage)
                Select Case iRotation
                    Case Is = 90
                        matrix2.Rotate(-iRotation)
                        matrix2.Translate(-oPdfOriginal.GetPageSize(iPage).Width, 0)
                    Case Is = 180 'Not tested yet.
                        matrix2.Rotate(-iRotation)
                        matrix2.Translate(-oPdfOriginal.GetPageSize(iPage).Width, -oPdfOriginal.GetPageSize(iPage).Height)
                    Case Is = 270 'Not tested yet.
                        matrix2.Rotate(-iRotation)
                        matrix2.Translate(0, oPdfOriginal.GetPageSize(iPage).Height)
                    Case Else
                End Select

                'Add the new layer ot this page.
                PDFDirectContent.BeginLayer(PDFNewLayer)
                PDFDirectContent.AddTemplate(iPageOriginal, matrix2)
                PDFDirectContent.EndLayer()
            Loop
            oPdfStamper.SetFullCompression()
            Return True
        Catch ex As Exception
            Return False
        Finally
            oPdfMarkup.Close()
            oPdfOriginal.Close()
            oPdfStamper.Close()
            matrix1.Dispose()
            matrix2.Dispose()
        End Try
    End Function

Code has been posted on Google Code http://code.google.com/p/pdflayermerger/

Many thanks to iText for the excellent library and to Lukasz Swiatkowski for the glass button component (http://www.codeproject.com/Articles/17695/Creating-a-Glass-Button-using-GDI).