cjhaas.com Basically a place that Chris can post solutions to problems so he can easily find them later

This post is in response to a comment here.

Let’s say you have a PDF with hyperlinks pointing to URLs like http://www.bing.com and you want to make these instead point to a page internal to the PDF. (Personally I can’t think of why this would be needed but someone apparently has this need.)

We’ll use the PDF annotation code that I posted on Stack Overflow here and modify it just a little bit. The code below is written in VB.Net 2010 and targets iTextSharp 5.1.2.0. See the individual code comments for specifics. If you have any questions you can leave a comment here but its probably faster to post your code and problems on Stack Overflow and just link to this post.

First, we’ll create some global variables to work with:

    ''//Folder that we are working in
    Private Shared ReadOnly WorkingFolder As String = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "Hyperlinked PDFs")
    ''//Pdf with sample hyperlinks
    Private Shared ReadOnly BaseFile As String = Path.Combine(WorkingFolder, "Base.pdf")
    ''//Pdf with adjusted hyperlinks
    Private Shared ReadOnly FinalFile As String = Path.Combine(WorkingFolder, "Final.pdf")

Next we’ll create a sample PDF that we can modify URLs with later. Nothing really special here, should be self-explanatory hopefully.

    Private Shared Sub CreateSamplePdf()
        ''//Create our output directory if it does not exist
        Directory.CreateDirectory(WorkingFolder)

        ''//Create our sample PDF
        Using Doc As New iTextSharp.text.Document(PageSize.LETTER)
            Using FS As New FileStream(BaseFile, FileMode.Create, FileAccess.Write, FileShare.Read)
                Using writer = PdfWriter.GetInstance(Doc, FS)
                    Doc.Open()

                    ''//Turn our hyperlinks blue
                    Dim BlueFont As Font = FontFactory.GetFont("Arial", 12, iTextSharp.text.Font.NORMAL, iTextSharp.text.BaseColor.BLUE)

                    ''//Create 10 pages with simple labels on them
                    For I = 1 To 10
                        Doc.NewPage()
                        Doc.Add(New Paragraph(String.Format("Page {0}", I)))
                        ''//On the first page add some links
                        If I = 1 Then
                           ''//Add an external link
                            Doc.Add(New Paragraph(New Chunk("Go to website", BlueFont).SetAction(New PdfAction("http://www.bing.com/", False))))

                            ''//Go to a specific hard-coded page number
                            Doc.Add(New Paragraph(New Chunk("Go to page 5", BlueFont).SetAction(PdfAction.GotoLocalPage(5, New PdfDestination(0), writer))))
                        End If
                    Next
                    Doc.Close()
                End Using
            End Using
        End Using
    End Sub

Lastly we’ll write some code to modify all of the external hyperlinks. The key here is to update the annotation’s dictionary reference for /S. A remote URL has a /URI (NOTE: the letter I and not L, “eye” not “el”) and we need to change this to /GOTO. The second trick is that the destination (/D) is an array, of which the first item is an indirect reference to the page that you want to go to and the second item is a fitting option.

    Private Shared Sub ListPdfLinks()

        ''//Setup some variables to be used later
        Dim R As PdfReader
        Dim PageCount As Integer
        Dim PageDictionary As PdfDictionary
        Dim Annots As PdfArray

        ''//Open our reader
        R = New PdfReader(BaseFile)
        ''//Get the page cont
        PageCount = R.NumberOfPages

        ''//Loop through each page
        For I = 1 To PageCount
            ''//Get the current page
            PageDictionary = R.GetPageN(I)

            ''//Get all of the annotations for the current page
            Annots = PageDictionary.GetAsArray(PdfName.ANNOTS)

            ''//Make sure we have something
            If (Annots Is Nothing) OrElse (Annots.Length = 0) Then Continue For

            ''//Loop through each annotation
            For Each A In Annots.ArrayList

                ''//Convert the itext-specific object as a generic PDF object
                Dim AnnotationDictionary = DirectCast(PdfReader.GetPdfObject(A), PdfDictionary)

                ''//Make sure this annotation has a link
                If Not AnnotationDictionary.Get(PdfName.SUBTYPE).Equals(PdfName.LINK) Then Continue For

                ''//Make sure this annotation has an ACTION
                If AnnotationDictionary.Get(PdfName.A) Is Nothing Then Continue For

                ''//Get the ACTION for the current annotation
                Dim AnnotationAction = DirectCast(AnnotationDictionary.Get(PdfName.A), PdfDictionary)

                ''//Test if it is a URI action. NOTE: URI and not URL
                If AnnotationAction.Get(PdfName.S).Equals(PdfName.URI) Then
                    ''//Remove the old action, I don't think this is actually necessary but I do it anyways
                    AnnotationAction.Remove(PdfName.S)
                    ''//Add a new action that is a GOTO action
                    AnnotationAction.Put(PdfName.S, PdfName.GOTO)
                    ''//The destination is an array containing an indirect reference to the page as well as a fitting option
                    Dim NewLocalDestination As New PdfArray()
                    ''//Link it to page 5
                    NewLocalDestination.Add(DirectCast(R.GetPageOrigRef(5), PdfObject))
                    ''//Set it to fit page
                    NewLocalDestination.Add(PdfName.FIT)
                    ''//Add the array to the annotation's destination (/D)
                    AnnotationAction.Put(PdfName.D, NewLocalDestination)
                End If
            Next
        Next

        ''//The above code modified an im-memory representation of a PDF, the code below writes these changes to disk
        Using FS As New FileStream(FinalFile, FileMode.Create, FileAccess.Write, FileShare.None)
            Using Doc As New Document()
                Using writer As New PdfCopy(Doc, FS)
                    Doc.Open()
                    For I = 1 To R.NumberOfPages
                        writer.AddPage(writer.GetImportedPage(R, I))
                    Next
                    Doc.Close()
                End Using
            End Using
        End Using
    End Sub

(I originally posted this on Stack Overflow)

iText and iTextSharp have some methods for replacing indirect objects. Specifically there’s PdfReader.KillIndirect() which does what it says and PdfWriter.AddDirectImageSimple(iTextSharp.text.Image, PRIndirectReference) which you can then use to replace what you killed off.

In pseudo C# code you’d do:

var oldImage = PdfReader.GetPdfObject();
var newImage = YourImageCompressionFunction(oldImage);
PdfReader.KillIndirect(oldImage);
yourPdfWriter.AddDirectImageSimple(newImage, (PRIndirectReference)oldImage);

Below is a full working C# 2010 WinForms app targeting iTextSharp 5.1.1.0. It takes an existing JPEG on your desktop called “LargeImage.jpg” and creates a new PDF from it. Then it opens the PDF, extracts the image, physically shrinks it to 90% of the original size, applies 85% JPEG compression and writes it back to the PDF. See the comments in the code for more of an explanation. The code needs lots more null/error checking. Also looks for NOTE comments where you’ll need to expand to handle other situations.

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
using System.Windows.Forms;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;

namespace WindowsFormsApplication1 {
    public partial class Form1 : Form {
        public Form1() {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e) {
            //Our working folder
            string workingFolder = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
            //Large image to add to sample PDF
            string largeImage = Path.Combine(workingFolder, "LargeImage.jpg");
            //Name of large PDF to create
            string largePDF = Path.Combine(workingFolder, "Large.pdf");
            //Name of compressed PDF to create
            string smallPDF = Path.Combine(workingFolder, "Small.pdf");

            //Create a sample PDF containing our large image, for demo purposes only, nothing special here
            using (FileStream fs = new FileStream(largePDF, FileMode.Create, FileAccess.Write, FileShare.None)) {
                using (Document doc = new Document()) {
                    using (PdfWriter writer = PdfWriter.GetInstance(doc, fs)) {
                        doc.Open();

                        iTextSharp.text.Image importImage = iTextSharp.text.Image.GetInstance(largeImage);
                        doc.SetPageSize(new iTextSharp.text.Rectangle(0, 0, importImage.Width, importImage.Height));
                        doc.SetMargins(0, 0, 0, 0);
                        doc.NewPage();
                        doc.Add(importImage);

                        doc.Close();
                    }
                }
            }

            //Now we're going to open the above PDF and compress things

            //Bind a reader to our large PDF
            PdfReader reader = new PdfReader(largePDF);
            //Create our output PDF
            using (FileStream fs = new FileStream(smallPDF, FileMode.Create, FileAccess.Write, FileShare.None)) {
                //Bind a stamper to the file and our reader
                using (PdfStamper stamper = new PdfStamper(reader, fs)) {
                    //NOTE: This code only deals with page 1, you'd want to loop more for your code
                    //Get page 1
                    PdfDictionary page = reader.GetPageN(1);
                    //Get the xobject structure
                    PdfDictionary resources = (PdfDictionary)PdfReader.GetPdfObject(page.Get(PdfName.RESOURCES));
                    PdfDictionary xobject = (PdfDictionary)PdfReader.GetPdfObject(resources.Get(PdfName.XOBJECT));
                    if (xobject != null) {
                        PdfObject obj;
                        //Loop through each key
                        foreach (PdfName name in xobject.Keys) {
                            obj = xobject.Get(name);
                            if (obj.IsIndirect()) {
                                //Get the current key as a PDF object
                                PdfDictionary imgObject = (PdfDictionary)PdfReader.GetPdfObject(obj);
                                //See if its an image
                                if (imgObject.Get(PdfName.SUBTYPE).Equals(PdfName.IMAGE)) {
                                    //NOTE: There's a bunch of different types of filters, I'm only handing the simplest one here which is basically raw JPG, you'll have to research others
                                    if (imgObject.Get(PdfName.FILTER).Equals(PdfName.DCTDECODE)) {
                                        //Get the raw bytes of the current image
                                        byte[] oldBytes = PdfReader.GetStreamBytesRaw((PRStream)imgObject);
                                        //Will hold bytes of the compressed image later
                                        byte[] newBytes;
                                        //Wrap a stream around our original image
                                        using (MemoryStream sourceMS = new MemoryStream(oldBytes)) {
                                            //Convert the bytes into a .Net image
                                            using (System.Drawing.Image oldImage = Bitmap.FromStream(sourceMS)) {
                                                //Shrink the image to 90% of the original
                                                using (System.Drawing.Image newImage = ShrinkImage(oldImage, 0.9f)) {
                                                    //Convert the image to bytes using JPG at 85%
                                                    newBytes = ConvertImageToBytes(newImage, 85);
                                                }
                                            }
                                        }
                                        //Create a new iTextSharp image from our bytes
                                        iTextSharp.text.Image compressedImage = iTextSharp.text.Image.GetInstance(newBytes);
                                        //Kill off the old image
                                        PdfReader.KillIndirect(obj);
                                        //Add our image in its place
                                        stamper.Writer.AddDirectImageSimple(compressedImage, (PRIndirectReference)obj);
                                    }
                                }
                            }
                        }
                    }
                }
            }

            this.Close();
        }

        //Standard image save code from MSDN, returns a byte array
        private static byte[] ConvertImageToBytes(System.Drawing.Image image, long compressionLevel) {
            if (compressionLevel < 0) {
                compressionLevel = 0;
            } else if (compressionLevel > 100) {
                compressionLevel = 100;
            }
            ImageCodecInfo jgpEncoder = GetEncoder(ImageFormat.Jpeg);

            System.Drawing.Imaging.Encoder myEncoder = System.Drawing.Imaging.Encoder.Quality;
            EncoderParameters myEncoderParameters = new EncoderParameters(1);
            EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder, compressionLevel);
            myEncoderParameters.Param[0] = myEncoderParameter;
            using (MemoryStream ms = new MemoryStream()) {
                image.Save(ms, jgpEncoder, myEncoderParameters);
                return ms.ToArray();
            }

        }
        //standard code from MSDN
        private static ImageCodecInfo GetEncoder(ImageFormat format) {
            ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();
            foreach (ImageCodecInfo codec in codecs) {
                if (codec.FormatID == format.Guid) {
                    return codec;
                }
            }
            return null;
        }
        //Standard high quality thumbnail generation from http://weblogs.asp.net/gunnarpeipman/archive/2009/04/02/resizing-images-without-loss-of-quality.aspx
        private static System.Drawing.Image ShrinkImage(System.Drawing.Image sourceImage, float scaleFactor) {
            int newWidth = Convert.ToInt32(sourceImage.Width * scaleFactor);
            int newHeight = Convert.ToInt32(sourceImage.Height * scaleFactor);

            var thumbnailBitmap = new Bitmap(newWidth, newHeight);
            using (Graphics g = Graphics.FromImage(thumbnailBitmap)) {
                g.CompositingQuality = CompositingQuality.HighQuality;
                g.SmoothingMode = SmoothingMode.HighQuality;
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                System.Drawing.Rectangle imageRectangle = new System.Drawing.Rectangle(0, 0, newWidth, newHeight);
                g.DrawImage(sourceImage, imageRectangle);
            }
            return thumbnailBitmap;
        }
    }
}