itext-modifying

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Java IText: Modifying Existing PDF Documents

By Jakob Jenkov

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Table of Contents

• Adding Content to the PDF Document

IText can modify existing PDF files in many different ways. Here I'll just cover one of the most used modifications - stamping an existing PDF with text or images. Get the book "IText in Action" to get the full story on manipulating existing PDF documents.

If you already have a finished PDF, and just want to add a header, footer or watermark to it, IText provides the com.itextpdf.pdf.PdfStamper class.

First you read the existing document using a PdfReader, then modify it using the PdfStamper.

Here is a simple code example:

import com.itextpdf.text.DocumentException;
import com.itextpdf.text.Image;
import com.itextpdf.text.pdf.PdfContentByte;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.PdfStamper;

import java.io.FileOutputStream;
import java.io.IOException;

public class PdfStamperExample {

  public static void main(String[] args) {
    try {
      PdfReader pdfReader = new PdfReader("HelloWorld.pdf");

      PdfStamper pdfStamper = new PdfStamper(pdfReader,
            new FileOutputStream("HelloWorld-Stamped.pdf"));

      Image image = Image.getInstance("watermark.png");

      for(int i=1; i<= pdfReader.getNumberOfPages(); i++){

          PdfContentByte content = pdfStamper.getUnderContent(i);

          image.setAbsolutePosition(100f, 700f);

          content.addImage(image);
      }

      pdfStamper.close();

    } catch (IOException e) {
      e.printStackTrace();
    } catch (DocumentException e) {
      e.printStackTrace();
    }
  }
}

Adding Content to the PDF Document

To add content to the document you need to access to a PdfContentByte from thePdfStamper. You can add content either above or below the existing content in the PDF document. Here is how you obtain the PdfContentByte from the PdfStamper.

PdfContentByte underContent = pdfStamper.getUnderContent(1);

PdfContentByte overContent  = pdfStamper.getOverContent(1);

The number passed as parameter is the page number of the page to get the under or over content for.

The PdfContentByte object has methods for adding all kinds of content to a PDF including text, graphics, images etc.