使用iTextSharp从PDF中删除水印
本文关键字：删除 PDF iTextSharp 使用 | 更新日期: 2023-09-27 18:19:45
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。我调查了iTextSharp，但没有得到任何帮助。我甚至试图添加水印作为图层，然后删除图层，但无法从pdf中删除图层的内容。我查看了iText中的层移除，发现了一个类OCGRemover，但在iTextsharp中找不到等效的类。
我将根据"我甚至试图将水印添加为层"这句话向您提出质疑，并假设您正在处理您正在创建的内容，而不是试图取消标记他人的内容。
PDF使用可选内容组（OCG）将对象存储为图层。如果你将水印文本添加到一个层中，你以后可以很容易地将其删除。
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。它使用的代码基于Bruno在这里找到的原始Java代码。代码分为三部分。第1节创建了一个示例PDF供我们使用。第2节从第一个创建一个新的PDF，并在单独的层上为每个页面应用水印。第3节从第二个创建了一个最终的PDF，但删除了带有水印文本的层。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，我找不到访问这个名称的方法，所以下面的代码在层中查找实际的水印文本。如果您不使用额外的PDF层，我建议只在内容流中查找/OC，不要浪费时间查找实际的水印文本。如果你能找到一种按名称查找/OC组的方法，请告诉我！
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答案的扩展，在这篇文章的底部包含了一个用于删除层的VB.Net类，这应该更精确一些。
- 它遍历PDF的图层列表（存储在文件目录中
OCProperties字典中的OCGs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），以找到指向层对象的属性（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的实例，从而可以适当地仅删除这些片段
然后，代码会尽可能多地清理所有引用。调用代码可能如图所示：
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
全类：
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