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c# - 使用 iTextSharp 从 PDF 中删除水印

转载 作者:行者123 更新时间:2023-12-01 05:36:27 26 4
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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 但无法获得任何帮助。我什至尝试添加水印作为图层,然后删除该图层,但无法从pdf中删除图层的内容。我研究了 iText 的图层移除功能,发现了一个类 OCGRemover,但我无法在 iTextsharp 中获得等效的类。

最佳答案

我将根据“我什至尝试将水印添加为图层”这一说法,对您进行无罪推定,并假设您正在处理自己正在创建的内容,而不是试图取消其他人的内容的水印。

PDF 使用可选内容组 (OCG) 将对象存储为图层。如果您将水印文本添加到图层中,以后可以很容易地将其删除。

下面的代码是面向 iTextSharp 5.1.1.0 的完整工作 C# 2010 WinForms 应用程序。它使用基于 Bruno's original Java code found here 的代码。该代码分为三部分。第 1 部分创建了一个示例 PDF 供我们使用。第 2 部分从第一个部分创建一个新的 PDF,并将水印应用到单独图层上的每个页面。第 3 部分根据第二个 PDF 创建最终 PDF,但删除带有水印文本的图层。有关更多详细信息,请参阅代码注释。

当您创建 PdfLayer 对象时,您可以为其指定一个名称以显示在 PDF 阅读器中。不幸的是,我找不到访问该名称的方法,因此下面的代码会查找图层内的实际水印文本。如果您没有使用其他 PDF 图层,我建议您在内容流中查找 /OC,而不是浪费时间查找实际的水印文本。如果您找到了按名称查找 /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();
}
}
}

关于c# - 使用 iTextSharp 从 PDF 中删除水印,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/8125296/

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