Add Text Watermarks to PDF

Watermark plays an important role in a lot of scenarios, and adding watermarks to PDF files can effectively protect your documents from unauthorized use. This article will share how to programmatically add a single-line text watermark to PDF using Free Spire.PDF for Java.

Installation (2 methods)

Method 1: Download the free library and unzip it. Then add the Spire.Pdf.jar file to your project as dependency.

Method 2: Directly add the jar dependency to maven project by adding the following configurations to the pom.xml.

<repositories>
    <repository>
        <id>com.e-iceblue</id>
        <name>e-iceblue</name>
        <url>https://repo.e-iceblue.com/nexus/content/groups/public/</url>
    </repository>
</repositories>
<dependencies>
    <dependency>
        <groupId>e-iceblue</groupId>
        <artifactId>spire.pdf.free</artifactId>
        <version>5.1.0</version>
    </dependency>
</dependencies>

Samle Code

Free Spire.PDF for Java does not provide a direct interface or class to add watermarks to PDF files. But you can draw text into a PDF page and set transparency to the text to mimic a watermark effect. The complete sample code is shown as below.

import com.spire.pdf.*;
import com.spire.pdf.graphics.*;
import java.awt.*;
import java.lang.Math;


public class TextWatermark {
    public static void main(String[] args) {
        //create a PdfDocument instance
        PdfDocument pdf = new PdfDocument();

        //load the sample document
        pdf.loadFromFile("E:\\Files\\template.pdf");
        PdfPageBase page = pdf.getPages().get(0);
        // Create a PdfTrueTypeFont object
        PdfTrueTypeFont font = new PdfTrueTypeFont(new Font("Arial", Font.PLAIN, 50), true);
        // Set the watermark text
        String text = "CONFIDENTIAL";
        // Measure the text size
        // Calculate the values of two offset variables,
        // which will be used to calculate the translation amount of the coordinate system
        float offset1 = ((float) ((font.measureString(text).getWidth()
                * (Math.sqrt(2) / 4))));
        float offset2 = ((float) ((font.measureString(text).getHeight()
                * (Math.sqrt(2) / 4))));

        // Set the page transparency
        page.getCanvas().setTransparency(0.5);
        // Translate the coordinate system by specified coordinates
        page.getCanvas().translateTransform(((page.getCanvas().getSize().getWidth() / 2)
                - (offset1 - offset2)), ((page.getCanvas().getSize().getHeight() / 2)
                + (offset1 - offset2)));
        // Rotate the coordinate system 45 degrees counterclockwise
        page.getCanvas().rotateTransform(-45);
        // Draw watermark text on the page
        page.getCanvas().drawString(text, font, PdfBrushes.getDarkGray(), 0, 0);


        // Save the changes to another file
        pdf.saveToFile("TextWatermark.pdf");
    }
}