使用iTextSharp从PDF中删除水印

Question

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,但我无法在iTextsharp中获得一个等效的类.

Answer 1

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.

下面的代码是一个针对iTextSharp 5.1.1.0的全功能C#2010 WinForms应用程序.它使用基于Bruno原始Java代码的代码.代码分为三个部分.第1节为我们创建了一个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.遗憾的是,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.如果你不使用额外的PDF图层我建议只想找/OC的内容流中,而不是浪费时间寻找你的实际水印文本.如果你找到了一个/OC按名称寻找群体的方法,请让我知道!

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();
        }
    }
}