private void button1_Click(object sender, EventArgs e)
        {
            if (openFileDialog1.ShowDialog() == System.Windows.Forms.DialogResult.Cancel) return;
            if (saveFileDialog1.ShowDialog() == System.Windows.Forms.DialogResult.Cancel) return;
 
           PdfDocument inputDocument1 = PdfReader.Open(openFileDialog1.FileName, PdfDocumentOpenMode.Import);
            PdfDocument outputDocument = new PdfDocument();

            for (int pageIndex = 0; pageIndex < inputDocument1.PageCount; pageIndex++)
            {
                ModifyLinks(inputDocument1, outputDocument, pageIndex);
            }

            outputDocument.Save(saveFileDialog1.FileName);

            MessageBox.Show(saveFileDialog1.FileName + " was successfully saved.");
        }


   static void ModifyLinks(PdfDocument inputDocument, PdfDocument outputDocument, int page)
        {
            PdfPage currPage = inputDocument.Pages[page];

            currPage = outputDocument.AddPage(currPage);
            if (currPage.Annotations.Count != 0)
            {
                for (int j = currPage.Annotations.Count - 1; j >= 0; j--)
                {
                    var annot = currPage.Annotations[j];

                    PdfItem item  = annot.Elements["/A"];

                    if (item != null)
                    {
                        var uri = ((item as PdfSharp.Pdf.Advanced.PdfReference).Value as PdfDictionary).Elements[@"/URI"] as PdfString;
                        ModifyLink(outputDocument, uri);
                    }                   
                }
            }
        }

  static void ModifyLink( PdfDocument outputDocument, PdfItem uri)
        {
            PdfDictionary dictJS = new PdfDictionary();
            dictJS.Elements["/S"] = new PdfName("/JavaScript");
            dictJS.Elements["/JS"] = new PdfStringObject(outputDocument, "app.launchURL(\"" + uri.ToString() + "\", true);");

            outputDocument.Internals.AddObject(dictJS);

            PdfDictionary dict = new PdfDictionary();
            PdfArray array = new PdfArray();
            dict.Elements["/Names"] = array;
            array.Elements.Add(new PdfString("EmbeddedJS"));
            array.Elements.Add(PdfInternals.GetReference(dictJS));
            outputDocument.Internals.AddObject(dict);

            PdfDictionary group = new PdfDictionary();
            group.Elements["/JavaScript"] = PdfInternals.GetReference(dict);

            outputDocument.Internals.Catalog.Elements["/Names"] = group;
        }