使用iTextSharp从PDF中删除水印
我使用Pdfstamper在pdf上添加了水印。 这是代码：
for (int pageIndex = 1; pageIndex <= pageCount; pageIndex++) { iTextSharp.text.Rectangle pageRectangle = reader.GetPageSizeWithRotation(pageIndex); PdfContentByte pdfData = stamper.GetUnderContent(pageIndex); pdfData.SetFontAndSize(BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.CP1252, BaseFont.NOT_EMBEDDED), watermarkFontSize); PdfGState graphicsState = new PdfGState(); graphicsState.FillOpacity = watermarkFontOpacity; pdfData.SetGState(graphicsState); pdfData.SetColorFill(iTextSharp.text.BaseColor.BLACK); pdfData.BeginText(); pdfData.ShowTextAligned(PdfContentByte.ALIGN_CENTER, "LipikaChatterjee", pageRectangle.Width / 2, pageRectangle.Height / 2, watermarkRotation); pdfData.EndText(); } 这很好用。 现在我想从我的pdf中删除这个水印。 我查看了iTextSharp，但未能得到任何帮助。 我甚至尝试将水印添加为图层，然后删除图层，但无法从pdf中删除图层的内容。 我查看了iText的图层删除，发现了一个OCGRemover类，但是我无法在iTextsharp中获得等效的类。
我将根据“我甚至尝试添加水印作为图层”这一说法向您提供疑问，并假设您正在处理您正在创建的内容而不是试图对其他人的内容进行水印。
PDF使用可选内容组（OCG）将对象存储为图层。 如果将水印文本添加到图层，则可以在以后轻松地将其删除。
下面的代码是一个完整的C＃2010 WinForms应用程序，目标是iTextSharp 5.1.1.0。 它使用基于Bruno原始Java代码的代码 。 代码分为三个部分。 第1部分为我们创建了一个PDF样本供我们使用。 第2节从第一部分创建一个新的PDF，并在单独的图层上为每个页面应用水印。 第3节从第二部分创建最终PDF，但使用我们的水印文本删除图层。 有关其他详细信息，请参阅代码注释
创建PdfLayer对象时，可以为其指定一个名称以显示在PDF阅读器中。 不幸的是我无法找到访问此名称的方法，因此下面的代码会查找图层中的实际水印文本。 如果您不使用其他PDF图层，我建议您只在内容流中查找/OC ，而不是浪费时间查找实际的水印文本。 如果你找到一种方法来寻找/OC组的名字，请让我kowow！
using System; 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) { string workingFolder = Environment.GetFolderPath(Environment.SpecialFolder.Desktop); string startFile = Path.Combine(workingFolder, "StartFile.pdf"); string watermarkedFile = Path.Combine(workingFolder, "Watermarked.pdf"); string unwatermarkedFile = Path.Combine(workingFolder, "Un-watermarked.pdf"); string watermarkText = "This is a test"; //SECTION 1 //Create a 5 page PDF, nothing special here using (FileStream fs = new FileStream(startFile, FileMode.Create, FileAccess.Write, FileShare.None)) { using (Document doc = new Document(PageSize.LETTER)) { using (PdfWriter witier = PdfWriter.GetInstance(doc, fs)) { doc.Open(); for (int i = 1; i <= 5; i++) { doc.NewPage(); doc.Add(new Paragraph(String.Format("This is page {0}", i))); } doc.Close(); } } } //SECTION 2 //Create our watermark on a separate layer. The only different here is that we are adding the watermark to a PdfLayer which is an OCG or Optional Content Group PdfReader reader1 = new PdfReader(startFile); using (FileStream fs = new FileStream(watermarkedFile, FileMode.Create, FileAccess.Write, FileShare.None)) { using (PdfStamper stamper = new PdfStamper(reader1, fs)) { int pageCount1 = reader1.NumberOfPages; //Create a new layer PdfLayer layer = new PdfLayer("WatermarkLayer", stamper.Writer); for (int i = 1; i <= pageCount1; i++) { iTextSharp.text.Rectangle rect = reader1.GetPageSize(i); //Get the ContentByte object PdfContentByte cb = stamper.GetUnderContent(i); //Tell the CB that the next commands should be "bound" to this new layer cb.BeginLayer(layer); cb.SetFontAndSize(BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.CP1252, BaseFont.NOT_EMBEDDED), 50); PdfGState gState = new PdfGState(); gState.FillOpacity = 0.25f; cb.SetGState(gState); cb.SetColorFill(BaseColor.BLACK); cb.BeginText(); cb.ShowTextAligned(PdfContentByte.ALIGN_CENTER, watermarkText, rect.Width / 2, rect.Height / 2, 45f); cb.EndText(); //"Close" the layer cb.EndLayer(); } } } //SECTION 3 //Remove the layer created above //First we bind a reader to the watermarked file, then strip out a bunch of things, and finally use a simple stamper to write out the edited reader PdfReader reader2 = new PdfReader(watermarkedFile); //NOTE, This will destroy all layers in the document, only use if you don't have additional layers //Remove the OCG group completely from the document. //reader2.Catalog.Remove(PdfName.OCPROPERTIES); //Clean up the reader, optional reader2.RemoveUnusedObjects(); //Placeholder variables PRStream stream; String content; PdfDictionary page; PdfArray contentarray; //Get the page count int pageCount2 = reader2.NumberOfPages; //Loop through each page for (int i = 1; i <= pageCount2; i++) { //Get the page page = reader2.GetPageN(i); //Get the raw content contentarray = page.GetAsArray(PdfName.CONTENTS); if (contentarray != null) { //Loop through content for (int j = 0; j < contentarray.Size; j++) { //Get the raw byte stream stream = (PRStream)contentarray.GetAsStream(j); //Convert to a string. NOTE, you might need a different encoding here content = System.Text.Encoding.ASCII.GetString(PdfReader.GetStreamBytes(stream)); //Look for the OCG token in the stream as well as our watermarked text if (content.IndexOf("/OC") >= 0 && content.IndexOf(watermarkText) >= 0) { //Remove it by giving it zero length and zero data stream.Put(PdfName.LENGTH, new PdfNumber(0)); stream.SetData(new byte[0]); } } } } //Write the content out using (FileStream fs = new FileStream(unwatermarkedFile, FileMode.Create, FileAccess.Write, FileShare.None)) { using (PdfStamper stamper = new PdfStamper(reader2, fs)) { } } this.Close(); } } }
作为Chris的答案的扩展，本post底部包含一个用于删除图层的VB.Net类，它应该更精确一些。
- 它遍历PDF的图层列表（存储在文件目录中
OCProperties字典中的OCProperties数组中）。 此数组包含对PDF文件中包含名称的对象的间接引用 - 它遍历页面的属性（也存储在字典中）以查找指向图层对象的属性（通过间接引用）
- 它对内容流进行实际解析，以查找模式
/OC /{PagePropertyReference} BDC {Actual Content} EMC实例，以便它可以根据需要仅删除这些段
然后代码尽可能地清理所有引用。 调用代码可能如下所示：
Public Shared Sub RemoveWatermark(path As String, savePath As String) Using reader = New PdfReader(path) Using fs As New FileStream(savePath, FileMode.Create, FileAccess.Write, FileShare.None) Using stamper As New PdfStamper(reader, fs) Using remover As New PdfLayerRemover(reader) remover.RemoveByName("WatermarkLayer") End Using End Using End Using End Using End Sub
全class：
Imports iTextSharp.text Imports iTextSharp.text.io Imports iTextSharp.text.pdf Imports iTextSharp.text.pdf.parser Public Class PdfLayerRemover Implements IDisposable Private _reader As PdfReader Private _layerNames As New List(Of String) Public Sub New(reader As PdfReader) _reader = reader End Sub Public Sub RemoveByName(name As String) _layerNames.Add(name) End Sub Private Sub RemoveLayers() Dim ocProps = _reader.Catalog.GetAsDict(PdfName.OCPROPERTIES) If ocProps Is Nothing Then Return Dim ocgs = ocProps.GetAsArray(PdfName.OCGS) If ocgs Is Nothing Then Return 'Get a list of indirect references to the layer information Dim layerRefs = (From l In (From i In ocgs Select Obj = DirectCast(PdfReader.GetPdfObject(i), PdfDictionary), Ref = DirectCast(i, PdfIndirectReference)) Where _layerNames.Contains(l.Obj.GetAsString(PdfName.NAME).ToString) Select l.Ref).ToList 'Get a list of numbers for these layer references Dim layerRefNumbers = (From l In layerRefs Select l.Number).ToList 'Loop through the pages Dim page As PdfDictionary Dim propsToRemove As IEnumerable(Of PdfName) For i As Integer = 1 To _reader.NumberOfPages 'Get the page page = _reader.GetPageN(i) 'Get the page properties which reference the layers to remove Dim props = _reader.GetPageResources(i).GetAsDict(PdfName.PROPERTIES) propsToRemove = (From k In props.Keys Where layerRefNumbers.Contains(props.GetAsIndirectObject(k).Number) Select k).ToList 'Get the raw content Dim contentarray = page.GetAsArray(PdfName.CONTENTS) If contentarray IsNot Nothing Then For j As Integer = 0 To contentarray.Size - 1 'Parse the stream data looking for references to a property pointing to the layer. Dim stream = DirectCast(contentarray.GetAsStream(j), PRStream) Dim streamData = PdfReader.GetStreamBytes(stream) Dim newData = GetNewStream(streamData, (From p In propsToRemove Select p.ToString.Substring(1))) 'Store data without the stream references in the stream If newData.Length <> streamData.Length Then stream.SetData(newData) stream.Put(PdfName.LENGTH, New PdfNumber(newData.Length)) End If Next End If 'Remove the properties from the page data For Each prop In propsToRemove props.Remove(prop) Next Next 'Remove references to the layer in the master catalog RemoveIndirectReferences(ocProps, layerRefNumbers) 'Clean up unused objects _reader.RemoveUnusedObjects() End Sub Private Shared Function GetNewStream(data As Byte(), propsToRemove As IEnumerable(Of String)) As Byte() Dim item As PdfLayer = Nothing Dim positions As New List(Of Integer) positions.Add(0) Dim pos As Integer Dim inGroup As Boolean = False Dim tokenizer As New PRTokeniser(New RandomAccessFileOrArray(New RandomAccessSourceFactory().CreateSource(data))) While tokenizer.NextToken If tokenizer.TokenType = PRTokeniser.TokType.NAME AndAlso tokenizer.StringValue = "OC" Then pos = CInt(tokenizer.FilePointer - 3) If tokenizer.NextToken() AndAlso tokenizer.TokenType = PRTokeniser.TokType.NAME Then If Not inGroup AndAlso propsToRemove.Contains(tokenizer.StringValue) Then inGroup = True positions.Add(pos) End If End If ElseIf tokenizer.TokenType = PRTokeniser.TokType.OTHER AndAlso tokenizer.StringValue = "EMC" AndAlso inGroup Then positions.Add(CInt(tokenizer.FilePointer)) inGroup = False End If End While positions.Add(data.Length) If positions.Count > 2 Then Dim length As Integer = 0 For i As Integer = 0 To positions.Count - 1 Step 2 length += positions(i + 1) - positions(i) Next Dim newData(length) As Byte length = 0 For i As Integer = 0 To positions.Count - 1 Step 2 Array.Copy(data, positions(i), newData, length, positions(i + 1) - positions(i)) length += positions(i + 1) - positions(i) Next Dim origStr = System.Text.Encoding.UTF8.GetString(data) Dim newStr = System.Text.Encoding.UTF8.GetString(newData) Return newData Else Return data End If End Function Private Shared Sub RemoveIndirectReferences(dict As PdfDictionary, refNumbers As IEnumerable(Of Integer)) Dim newDict As PdfDictionary Dim arrayData As PdfArray Dim indirect As PdfIndirectReference Dim i As Integer For Each key In dict.Keys newDict = dict.GetAsDict(key) arrayData = dict.GetAsArray(key) If newDict IsNot Nothing Then RemoveIndirectReferences(newDict, refNumbers) ElseIf arrayData IsNot Nothing Then i = 0 While i < arrayData.Size indirect = arrayData.GetAsIndirectObject(i) If refNumbers.Contains(indirect.Number) Then arrayData.Remove(i) Else i += 1 End If End While End If Next End Sub #Region "IDisposable Support" Private disposedValue As Boolean ' To detect redundant calls ' IDisposable Protected Overridable Sub Dispose(disposing As Boolean) If Not Me.disposedValue Then If disposing Then RemoveLayers() End If ' TODO: free unmanaged resources (unmanaged objects) and override Finalize() below. ' TODO: set large fields to null. End If Me.disposedValue = True End Sub ' TODO: override Finalize() only if Dispose(ByVal disposing As Boolean) above has code to free unmanaged resources. 'Protected Overrides Sub Finalize() ' ' Do not change this code. Put cleanup code in Dispose(ByVal disposing As Boolean) above. ' Dispose(False) ' MyBase.Finalize() 'End Sub ' This code added by Visual Basic to correctly implement the disposable pattern. Public Sub Dispose() Implements IDisposable.Dispose ' Do not change this code. Put cleanup code in Dispose(ByVal disposing As Boolean) above. Dispose(True) GC.SuppressFinalize(Me) End Sub #End Region End Class