Add a Digital Signature to PDF Using Java

The digital signature in a PDF document guarantees the authenticity and integrity of the document, and it also helps prove that the original document has not been changed in any way during transmission. Nowadays, the digital signatures are widely used in e-commerce, software distribution, financial transactions and other fields. In this article, I will introduce how to use a free Java API to add a digital signature to an existing PDF document.

1# Import the jar dependency of the free Java API (2 Method)
● Download the free API (Free Spire.PDF for Java) and unzip it.Then add the Spire.Pdf.jar file to your project as dependency.

● 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>http://repo.e-iceblue.com/nexus/content/groups/public/</url>
        </repository>
</repositories>
<dependencies>
    <dependency>
        <groupId>e-iceblue</groupId>
        <artifactId>spire.pdf.free</artifactId>
        <version>4.3.0</version>
    </dependency>
</dependencies>

2# The sample code is shown below

import com.spire.pdf.PdfDocument;
import com.spire.pdf.graphics.PdfFont;
import com.spire.pdf.graphics.PdfFontFamily;
import com.spire.pdf.graphics.PdfFontStyle;
import com.spire.pdf.graphics.PdfImage;
import com.spire.pdf.security.GraphicMode;
import com.spire.pdf.security.PdfCertificate;
import com.spire.pdf.security.PdfCertificationFlags;
import com.spire.pdf.security.PdfSignature;

import java.awt.*;
import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;

public class AddDigitalSignature {

    public static void main(String[] args) {

        //Load a pdf document
        PdfDocument doc = new PdfDocument();
        doc.loadFromFile("C:\\Users\\Administrator\\Desktop\\Moon.pdf");

        //Load the certificate
        PdfCertificate cert = new PdfCertificate("F:\\pfx\\output\\Test.pfx", "111");

        //Create a PdfSignature object and specify its position and size
        PdfSignature signature = new PdfSignature(doc, doc.getPages().get(0), cert, "MySignature");
        Rectangle2D rect = new Rectangle2D.Float();
        rect.setFrame(new Point2D.Float((float) doc.getPages().get(0).getActualSize().getWidth() - 380, (float) doc.getPages().get(0).getActualSize().getHeight() - 120), new Dimension(250, 150));
        signature.setBounds(rect);

        //Set the graphics mode
        signature.setGraphicMode(GraphicMode.Sign_Image_And_Sign_Detail);

        //Set the signature content
        signature.setNameLabel("Signer:");
        signature.setName("Jessie");
        signature.setContactInfoLabel("ContactInfo:");
        signature.setContactInfo("xxxxxxxxx");
        signature.setDateLabel("Date:");
        signature.setDate(new java.util.Date());
        signature.setLocationInfoLabel("Location:");
        signature.setLocationInfo("Florida");
        signature.setReasonLabel("Reason: ");
        signature.setReason("The certificate of this document");
        signature.setDistinguishedNameLabel("DN: ");
        signature.setDistinguishedName(signature.getCertificate().get_IssuerName().getName());
        signature.setSignImageSource(PdfImage.fromFile("C:\\Users\\Administrator\\Desktop\\cert.jpg"));

        //Set the signature font
        signature.setSignDetailsFont(new PdfFont(PdfFontFamily.Helvetica, 10f, PdfFontStyle.Bold));

        //Set the document permission
        signature.setDocumentPermissions(PdfCertificationFlags.Forbid_Changes);
        signature.setCertificated(true);

        //Save to file
        doc.saveToFile("AddSignature.pdf");
        doc.close();
    }
}

3# A snapshot of the generated PDF document