使用 ITextSharp 编辑 PDF 中的超链接和锚点

Question

我正在使用 iTextSharp 库和 C#.Net 来分割我的 PDF 文件。

考虑一个名为 example.pdf 的 PDF 文件，包含 72 页。此sample.pdf 包含具有导航到其他页面的超链接的页面。例如：第 4 页有 3 个超链接，点击分别导航到相应的第 24、27、28 页。与第 4 页一样，有近 12 个页面带有此超链接。

现在使用 iTextSharp 库，我已将此 PDF 页面拆分为 72 个单独的文件，并以名称保存为 1.pdf,2.pdf....72.pdf。因此，在 4.pdf 中，当单击该超链接时，我需要使 PDF 导航到 24.pdf、27.pdf、28.pdf。

请帮我一下。如何编辑和设置 4.pdf 中的超链接，以便它导航到相应的 pdf 文件。

谢谢你， 阿肖克

Answer 1

你想要的东西是完全有可能的。您想要的将需要您使用低级 PDF 对象（PdfDictionary、PdfArray 等）。

每当有人需要使用这些对象时，我总是将他们参考 PDF 参考。对于您的情况，您需要检查第 7 章（特别是第 3 节）和第 12 章的第 3 节（文档级导航）和第 5 节（注释）。

假设您已经阅读了本文，那么您需要执行以下操作：

1. 逐步浏览每个页面的注释数组（在原始文档中，在分解之前）。
   1. 查找所有链接注释&他们的目的地。
   2. 为该链接构建与新文件对应的新目标。
   3. 将新目的地写入链接注释中。
2. 使用 PdfCopy 将此页面写入新的 PDF（它将复制注释以及页面内容）。

步骤 1.1 并不简单。有几种不同类型的“本地转到”注释格式。您需要确定给定链接指向哪个页面。有些链接可能会说 PDF 相当于“下一页”或“上一页”，而其他链接可能会包含对特定页面的引用。这将是“间接对象引用”，而不是页码。

要从页面引用确定页码，您需要......哎呀。好的。最有效的方法是为原始文档中的每个页面调用 PdfReader.GetPageRef(int pageNum) 并将其缓存在地图中（reference->pageNum）。

然后，您可以通过创建远程转到 PdfAction 并将其写入链接注释的“A”（操作）条目来构建“远程转到”链接，删除之前存在的任何内容（可能是“Dest”）。

我不太会说 C#，所以我将把实际的实现留给你。

Answer 2

好吧，基于 @Mark Storer 这里有一些起始代码。第一种方法创建一个包含 10 页的示例 PDF，并且第一页上有一些链接可以跳转到 PDF 的不同部分，以便我们可以使用一些内容。第二种方法打开第一种方法中创建的 PDF，并遍历每个注释，尝试找出注释链接到的页面并将其输出到 TRACE 窗口。代码采用 VB 编写，但如果需要，应该可以轻松转换为 C#。它的目标是 iTextSharp 5.1.1.0。

如果有机会，我可能会尝试更进一步，实际上拆分并重新链接事物，但我现在没有时间。

Option Explicit On
Option Strict On

Imports iTextSharp.text
Imports iTextSharp.text.pdf
Imports System.IO

Public Class Form1
    ''//Folder that we are working in
    Private Shared ReadOnly WorkingFolder As String = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "Hyperlinked PDFs")
    ''//Sample PDF
    Private Shared ReadOnly BaseFile As String = Path.Combine(WorkingFolder, "Sample.pdf")

    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

                            ''//Go to pages relative to this page
                            Doc.Add(New Paragraph(New Chunk("First Page", BlueFont).SetAction(New PdfAction(PdfAction.FIRSTPAGE))))

                            Doc.Add(New Paragraph(New Chunk("Next Page", BlueFont).SetAction(New PdfAction(PdfAction.NEXTPAGE))))

                            Doc.Add(New Paragraph(New Chunk("Prev Page", BlueFont).SetAction(New PdfAction(PdfAction.PREVPAGE)))) ''//This one does not make sense but is here for completeness

                            Doc.Add(New Paragraph(New Chunk("Last Page", BlueFont).SetAction(New PdfAction(PdfAction.LASTPAGE))))

                            ''//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
    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

                ''//I do not completely understand this but I think this turns an Indirect Reference into an actual object, but I could be wrong
                ''//Anyway, 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 named actions such as /FIRST, /LAST, etc
                If AnnotationAction.Get(PdfName.S).Equals(PdfName.NAMED) Then
                    Trace.Write("GOTO:")
                    If AnnotationAction.Get(PdfName.N).Equals(PdfName.FIRSTPAGE) Then
                        Trace.WriteLine(1)
                    ElseIf AnnotationAction.Get(PdfName.N).Equals(PdfName.NEXTPAGE) Then
                        Trace.WriteLine(Math.Min(I + 1, PageCount)) ''//Any links that go past the end of the document should just go to the last page
                    ElseIf AnnotationAction.Get(PdfName.N).Equals(PdfName.LASTPAGE) Then
                        Trace.WriteLine(PageCount)
                    ElseIf AnnotationAction.Get(PdfName.N).Equals(PdfName.PREVPAGE) Then
                        Trace.WriteLine(Math.Max(I - 1, 1)) ''//Any links the go before the first page should just go to the first page
                    End If


                    ''//Otherwise see if its a GOTO page action
                ElseIf AnnotationAction.Get(PdfName.S).Equals(PdfName.GOTO) Then

                    ''//Make sure that it has a destination
                    If AnnotationAction.GetAsArray(PdfName.D) Is Nothing Then Continue For

                    ''//Once again, not completely sure if this is the best route but the ACTION has a sub DESTINATION object that is an Indirect Reference.
                    ''//The code below gets that IR, asks the PdfReader to convert it to an actual page and then loop through all of the pages
                    ''//to see which page the IR points to. Very inneficient but I could not find a way to get the page number based on the IR.

                    ''//AnnotationAction.GetAsArray(PdfName.D) gets the destination
                    ''//AnnotationAction.GetAsArray(PdfName.D).ArrayList(0) get the indirect reference part of the destination (.ArrayList(1) has fitting options)
                    ''//DirectCast(AnnotationAction.GetAsArray(PdfName.D).ArrayList(0), PRIndirectReference) turns it into a PRIndirectReference
                    ''//The full line gets us an actual page object (actually I think it could be any type of pdf object but I have not tested that).
                    ''//BIG NOTE: This line really should have a bunch more sanity checks in place
                    Dim AnnotationReferencedPage = PdfReader.GetPdfObject(DirectCast(AnnotationAction.GetAsArray(PdfName.D).ArrayList(0), PRIndirectReference))
                    Trace.Write("GOTO:")
                    ''//Re-loop through all of the pages in the main document comparing them to this page
                    For J = 1 To PageCount
                        If AnnotationReferencedPage.Equals(R.GetPageN(J)) Then
                            Trace.WriteLine(J)
                            Exit For
                        End If
                    Next
                End If
            Next
        Next
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        CreateSamplePdf()
        ListPdfLinks()
        Me.Close()
    End Sub
End Class

Answer 3

下面的这个函数使用 iTextSharp 来：

1. 打开 PDF
2. 通过 PDF
3. 页面检查每个页面上的注释是否有锚点

第 4 步是在此处插入您想要的任何逻辑...更新链接、记录它们等。

    /// <summary>Inspects PDF files for internal links.
    /// </summary>
    public static void FindPdfDocsWithInternalLinks()
    {
        foreach (var fi in PdfFiles) {
            try {
                var reader = new PdfReader(fi.FullName);
                // Pagination
                for(var i = 1; i <= reader.NumberOfPages; i++) {
                    var pageDict = reader.GetPageN(i);
                    var annotArray = (PdfArray)PdfReader.GetPdfObject(pageDict.Get(PdfName.ANNOTS));
                    if (annotArray == null) continue;
                    if (annotArray.Length <= 0) continue;
                    // check every annotation on the page
                    foreach (var annot in annotArray.ArrayList) {
                        var annotDict = (PdfDictionary)PdfReader.GetPdfObject(annot);
                        if (annotDict == null) continue;
                        var subtype = annotDict.Get(PdfName.SUBTYPE).ToString();
                        if (subtype != "/Link") continue;
                        var linkDict = (PdfDictionary)annotDict.GetDirectObject(PdfName.A);
                        if (linkDict == null) continue;
                        // if it makes it this far, its an Anchor annotation
                        // so we can grab it's URI
                        var sUri = linkDict.Get(PdfName.URI).ToString();
                        if (String.IsNullOrEmpty(sUri)) continue;
                    }
                }
                reader.Close();
            }
            catch (InvalidPdfException e)
            {
                if (!fi.FullName.Contains("_vti_cnf"))
                    Console.WriteLine("\r\nInvalid PDF Exception\r\nFilename: " + fi.FullName + "\r\nException:\r\n" + e);
                continue;
            }
            catch (NullReferenceException e) 
            {
                if (!fi.FullName.Contains("_vti_cnf"))
                    Console.WriteLine("\r\nNull Reference Exception\r\nFilename: " + fi.Name + "\r\nException:\r\n" + e);
                continue;
            }
        }

        // DO WHATEVER YOU WANT HERE
    }

好运气。