Adding a Graphical Seal and Network Timestamp Electronic Signature to PDF Documents with Java and Spire

Electronic seals are commonly seen on digital invoices and contracts; they combine a visual seal image with a timestamped electronic signature that complies with the Chinese Electronic Signature Law, giving the document legal effect.

The following example shows how to add such a seal and a network timestamp signature to a PDF using Java and the Spire framework. Before starting, you need a .pfx digital certificate file and a PNG image of the seal.

Step 1: Load the PDF document

PdfDocument pdf = new PdfDocument();
String filename = "~/Tmp/Window.pdf";
System.out.println(new File(filename).exists());
pdf.loadFromFile(filename);

Step 2: Load the certificate and create the signature object

String caFile = "/Users/walker/Tmp/certifation2/server.pfx";
PdfCertificate cert = new PdfCertificate(caFile, "likuo.dev");
PdfSignature signature = new PdfSignature(pdf, pdf.getPages().get(1), cert, "电子数据签名");

Step 3: Define the signature position and size on the page

PdfSignature signature = new PdfSignature(pdf, pdf.getPages().get(1), cert, "电子数据签名");
Rectangle2D rect = new Rectangle2D.Float();
float x = (float) (pdf.getPages().get(0).getActualSize().getWidth() - 340);
float y = (float) (pdf.getPages().get(0).getActualSize().getHeight() - 230);
Dimension dimension = new Dimension(300, 150);
Point2D point2D = new Point2D.Float(x, y);
rect.setFrame(point2D, dimension);
signature.setBounds(rect);

Step 4: Configure a trusted timestamp service

String timestampeServerUrl = "http://timestamp.digicert.com";
signature.configureTimestamp(timestampeServerUrl);

Step 5: Set signature visual details

signature.setGraphicMode(GraphicMode.Sign_Image_And_Sign_Detail);
signature.setNameLabel("名称：");
signature.setName("李xxx");
signature.setDateLabel("日期：");
signature.setDate(new java.util.Date());
signature.setLocationInfoLabel("地点：");
signature.setLocationInfo("北京市-北京市");
signature.setReasonLabel("原由：");
signature.setReason("电子xxx合同");
signature.setDistinguishedNameLabel("DN: ");
signature.setDistinguishedName(signature.getCertificate().get_IssuerName().getName());
signature.setDistinguishedNameLabel("序列：");
signature.setDistinguishedName("20210813第【李】23次");
signature.setSignImageSource(PdfImage.fromFile("～.png"));

Step 6: Set font and document permissions

signature.setSignDetailsFont(new PdfTrueTypeFont(new Font("Arial Unicode MS", Font.PLAIN, 9)));
signature.setDocumentPermissions(PdfCertificationFlags.Forbid_Changes);
signature.setCertificated(true);

Step 7: Save the signed PDF

File file = new File(filename);
String fileName = file.getName();
if (fileName.contains(".")) {
    pdf.saveToFile(fileName.substring(0, fileName.indexOf(".")) + "_Sign.pdf");
} else {
    pdf.saveToFile(fileName + "_Sign.pdf");
}
pdf.close();

After completing these steps, the PDF contains a network‑timestamped electronic signature, which helps verify document integrity, origin, and protects intellectual property, making it suitable for electronic invoices, contracts, and forensic evidence.