Java로 PDF에 디지털 서명을 추가하는 방법

Prerequisites

To digitally sign PDF documents, the following prerequisites are required:

• Any Java IDE (NetBeans, Eclipse, IntelliJ) Installed - This article will use IntelliJ. You can separately download the Java Development Kit from the Oracle Java SE Downloads.
• Maven Java Project for Automation - This will help download and manage dependencies in your Java program. You can download Maven from the Apache Maven Download Page.
• IronPDF Library Downloaded and Installed - To download and install IronPDF, include its Maven dependency artifact. You can add the following code snippet in the pom.xml file dependencies tag:

<dependency>
    <groupId>com.ironsoftware</groupId>
    <artifactId>ironpdf</artifactId>
    <version>2023.2.0</version>
</dependency>

<dependency>
    <groupId>com.ironsoftware</groupId>
    <artifactId>ironpdf</artifactId>
    <version>2023.2.0</version>
</dependency>

• Another dependency required is Slf4j-simple. It is optional and can be added using the following dependency in the pom.xml file:

  <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-simple</artifactId>
      <version>2.0.5</version>
  </dependency>

  <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-simple</artifactId>
      <version>2.0.5</version>
  </dependency>

  XML

pom.xml file

IronPDF Import Java Packages

The following imports are required in the main file. It allows using IronPDF functions to add a digital signature to a PDF document:

import com.ironsoftware.ironpdf.PdfDocument;
import com.ironsoftware.ironpdf.signature.Signature;
import com.ironsoftware.ironpdf.signature.SignatureManager;
import java.io.IOException;
import java.nio.file.Paths;

import com.ironsoftware.ironpdf.PdfDocument;
import com.ironsoftware.ironpdf.signature.Signature;
import com.ironsoftware.ironpdf.signature.SignatureManager;
import java.io.IOException;
import java.nio.file.Paths;

Now, everything required is done and ready to add a digital signature to PDF documents in Java using IronPDF.

Create PDF File or Open Existing PDF File

To Learn How to Digitally Sign PDFs, it is necessary to either create a PDF document from scratch or open an existing PDF document. This article will create a new PDF document for PDF signature using the renderHtmlAsPdf Method of the PdfDocument Class. The code goes as follows:

PdfDocument pdf = PdfDocument.renderHtmlAsPdf("<h1>Testing 2048 bit digital security</h1>");

PdfDocument pdf = PdfDocument.renderHtmlAsPdf("<h1>Testing 2048 bit digital security</h1>");

The PDF document is created but not saved yet. So, the next step is to create a digital signature and then add it to this PDF document and then finally save it.

Create a Digital Signature

You will have to create a digital signature certificate using Adobe Reader, which will be used in Java code to digitally sign PDF documents with those details. You can have a look at How to Create a Digital Signature in Adobe Reader.

Open Adobe Reader and click on Edit > Preferences. Then click on Signatures and like more on Identities and Trusted Certificates.

The project preferences

Add the following Signature field to make the .pfx or .p12 file doc.

Add Digital ID dialog

The following code sample will create a new signature in Java code using the .pfx certificate file for Windows and .p12 file for Mac along with its private key (password):

Signature signature = new Signature("Iron.pfx", "123456");

Signature signature = new Signature("Iron.pfx", "123456");

Sign PDF File with Digital Signature

IronPDF helps with adding the signature certificate using the SignatureManager class. [getSignature Method](/java/object-reference/api/com/ironsoftware/ironpdf/PdfDocument.html#getSignature()) helps to get the previous signature of the PDF document, and then a new signature can be added using the SignPdfWithSignature Method with the signature file as an argument. The code goes as follows:

SignatureManager signatureManager = pdf.getSignature();
signatureManager.SignPdfWithSignature(signature);

SignatureManager signatureManager = pdf.getSignature();
signatureManager.SignPdfWithSignature(signature);

Save PDF Signature File

Finally, let's save the PDF file; otherwise, the PDF is not signed by using the saveAs Method of the PdfDocument class. The code is simple and as follows:

pdf.saveAs("signed.pdf");

pdf.saveAs("signed.pdf");

On successful compilation and execution of the code, the output produces a PDF that has been digitally signed.

The output PDF file

IronPDF also provides other signing options, which are optional and can also be used for digital signatures. It includes signature images in the form of handwriting, computer-generated text images, or digitized images. The following code sample helps you add some additional security options for digital signing:

signature.setSigningContact("support@ironsoftware.com");
signature.setSigningLocation("Chicago, USA");
signature.setSigningReason("To show how to sign a PDF");
BufferedImage signatureImage = ImageIO.read(new File("handwriting.png"));
WritableRaster raster = signatureImage.getRaster();
DataBufferByte data = (DataBufferByte) raster.getDataBuffer();
signature.setSignatureImage(data.getData());

signature.setSigningContact("support@ironsoftware.com");
signature.setSigningLocation("Chicago, USA");
signature.setSigningReason("To show how to sign a PDF");
BufferedImage signatureImage = ImageIO.read(new File("handwriting.png"));
WritableRaster raster = signatureImage.getRaster();
DataBufferByte data = (DataBufferByte) raster.getDataBuffer();
signature.setSignatureImage(data.getData());

The complete code goes as follows:

import com.ironsoftware.ironpdf.PdfDocument;
import com.ironsoftware.ironpdf.signature.Signature;
import com.ironsoftware.ironpdf.signature.SignatureManager;

import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;
import java.awt.image.WritableRaster;
import java.io.File;
import java.io.IOException;

public class DigitalSignatureExample {
    public static void main(String[] args) throws IOException {

        // Step 1. Create a PDF File Doc
        PdfDocument pdf = PdfDocument.renderHtmlAsPdf("<h1>Testing 2048 bit digital security</h1>");

        // Step 2. Create a Signature.
        Signature signature = new Signature("Iron.pfx", "123456");

        // Step 3. Sign the PDF with the PdfSignature.
        SignatureManager signatureManager = pdf.getSignature();
        signatureManager.SignPdfWithSignature(signature);

        // Step 4. The PDF is not signed until saved to file, stream, or byte array.
        pdf.saveAs("signed.pdf");
    }
}

import com.ironsoftware.ironpdf.PdfDocument;
import com.ironsoftware.ironpdf.signature.Signature;
import com.ironsoftware.ironpdf.signature.SignatureManager;

import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;
import java.awt.image.WritableRaster;
import java.io.File;
import java.io.IOException;

public class DigitalSignatureExample {
    public static void main(String[] args) throws IOException {

        // Step 1. Create a PDF File Doc
        PdfDocument pdf = PdfDocument.renderHtmlAsPdf("<h1>Testing 2048 bit digital security</h1>");

        // Step 2. Create a Signature.
        Signature signature = new Signature("Iron.pfx", "123456");

        // Step 3. Sign the PDF with the PdfSignature.
        SignatureManager signatureManager = pdf.getSignature();
        signatureManager.SignPdfWithSignature(signature);

        // Step 4. The PDF is not signed until saved to file, stream, or byte array.
        pdf.saveAs("signed.pdf");
    }
}

You can check more information on Digital Signature from the PDF Signatures Code Example. If you want to add more security and even edit metadata, then check the Security and Metadata Code Example.