Cross-page seals, frequently utilized in legal contracts and bidding documents, span across adjacent pages to verify document integrity and prevent unauthorized page insertion or removal. Implementing this feature programmatically requires splitting a single seal graphic into equal segments and rendering each segment along the binding edge of consecutive PDF pages.

Dependency Configuration

To manipulate PDF structures and render graphics, include the Free Spire.PDF for Java library. For Maven-based projects, add the repository and dependency to your pom.xml:

<repositories>
    <repository>
        <id>com.e-iceblue</id>
        <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>3.9.0</version>
    </dependency>
</dependencies>

Implementation Logic

The workflow loads the target PDF, determines the total page count, slices the source seal image horizontally, and draws each slice on the right margin of its corresponding page. The vertical alignment is centered, while the horizontal alignment anchors to the page boundary.

import com.spire.pdf.PdfDocument;
import com.spire.pdf.PdfPageBase;
import com.spire.pdf.graphics.PdfGraphicsUnit;
import com.spire.pdf.graphics.PdfImage;
import com.spire.pdf.graphics.PdfUnitConvertor;

import javax.imageio.ImageIO;
import java.awt.geom.Point2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class PdfSeamStampProcessor {

    public static void main(String[] args) {
        String sourcePdf = "contract_draft.pdf";
        String sealFile = "official_seal.png";
        String targetPdf = "stamped_contract.pdf";

        try {
            applyCrossPageSeal(sourcePdf, sealFile, targetPdf);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void applyCrossPageSeal(String pdfPath, String imagePath, String outputPath) throws IOException {
        PdfDocument pdfDoc = new PdfDocument();
        pdfDoc.loadFromFile(pdfPath);

        int totalPages = pdfDoc.getPages().getCount();
        if (totalPages == 0) return;

        BufferedImage[] sealSegments = partitionSealImage(imagePath, totalPages);
        PdfUnitConvertor unitConverter = new PdfUnitConvertor();

        for (int pageIndex = 0; pageIndex < totalPages; pageIndex++) {
            PdfPageBase currentPage = pdfDoc.getPages().get(pageIndex);
            BufferedImage segment = sealSegments[pageIndex];

            // Convert pixel dimensions to PDF points (1/72 inch)
            float segmentWidthPts = unitConverter.convertUnits(
                    segment.getWidth(), PdfGraphicsUnit.Pixel, PdfGraphicsUnit.Point);

            // Calculate coordinates: right-aligned, vertically centered
            float posX = (float) currentPage.getSize().getWidth() - segmentWidthPts;
            float posY = (float) currentPage.getSize().getHeight() / 2;

            PdfImage pdfImg = PdfImage.fromImage(segment);
            currentPage.getCanvas().drawImage(pdfImg, new Point2D.Float(posX, posY));
        }

        pdfDoc.saveToFile(outputPath);
        pdfDoc.close();
    }

    private static BufferedImage[] partitionSealImage(String filePath, int divisions) throws IOException {
        BufferedImage original = ImageIO.read(new File(filePath));
        int sliceWidth = original.getWidth() / divisions;
        int sliceHeight = original.getHeight();
        BufferedImage[] slices = new BufferedImage[divisions];

        for (int i = 0; i < divisions; i++) {
            slices[i] = original.getSubimage(i * sliceWidth, 0, sliceWidth, sliceHeight);
        }
        return slices;
    }
}

Coordinate Calculation and Image Slicing

The partitionSealImage routine divides the source graphic horizontally based on the document's page count. Utilizing BufferedImage.getSubimage generates lightweight raster views without duplicating pixel data in memory. During the rendering phase, PdfUnitConvertor bridges the resoultion gap between standard screen pixels and PDF points, guaranteeing precise placement. The horizontal coordinate subtracts the converted slice width from the total page width, locking the stamp to the right edge. The vertical coordinate targets the exact midpoint of the page canvas. Once all segments are painted onto their respective pages, the modified document is serialized to the specified output path.