Removing Watermark from a PDF using iTextSharp

Question

I added a watermark on pdf using Pdfstamper. Here is the code:

for (int pageIndex = 1; pageIndex <= pageCount; pageIndex++)
{
    iTextSharp.text.Rectangl         


        

Answer 1

I'm going to give you the benefit of the doubt based on the statement "I even tried to add watermark as layer" and assume that you are working on content that you are creating and not trying to unwatermark someone else's content.

PDFs use Optional Content Groups (OCG) to store objects as layers. If you add your watermark text to a layer you can fairly easily remove it later.

The code below is a full working C# 2010 WinForms app targeting iTextSharp 5.1.1.0. It uses code based on Bruno's original Java code found here. The code is in three sections. Section 1 creates a sample PDF for us to work with. Section 2 creates a new PDF from the first and applies a watermark to each page on a separate layer. Section 3 creates a final PDF from the second but removes the layer with our watermark text. See the code comments for additional details.

When you create a PdfLayer object you can assign it a name to appear within a PDF reader. Unfortunately I can't find a way to access this name so the code below looks for the actual watermark text within the layer. If you aren't using additional PDF layers I would recommend only looking for /OC within the content stream and not wasting time looking for your actual watermark text. If you find a way to look for /OC groups by name please let me kwow!

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();
        }
    }
}