How to Add Watermarks to PDF Files Using Spring Boot and Java Libraries

PDF (Portable Document Format) is widely used, and adding watermarks can improve document identification and protect copyright. This guide shows how to implement PDF watermarking in a Spring Boot environment using several Java libraries and tools.

Method 1: Apache PDFBox

PDFBox is a free, open‑source Java library for creating and manipulating PDFs. Add the dependency to pom.xml :

<dependency>
    <groupId>org.apache.pdfbox</groupId>
    <artifactId>pdfbox</artifactId>
    <version>2.0.24</version>
</dependency>

Load the original PDF, iterate over pages, and use PDPageContentStream to draw the watermark text:

PDDocument document = PDDocument.load(new File("original.pdf"));
for (int i = 0; i < document.getNumberOfPages(); i++) {
    PDPage page = document.getPage(i);
    PDPageContentStream cs = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.APPEND, true, true);
    cs.setFont(PDType1Font.HELVETICA_BOLD, 36);
    cs.setNonStrokingColor(200, 200, 200);
    cs.beginText();
    cs.newLineAtOffset(100, 100);
    cs.showText("Watermark");
    cs.endText();
    cs.close();
}
document.save(new File("output.pdf"));
document.close();

Method 2: iText

iText is another popular Java PDF library. Add the Maven dependency:

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itextpdf</artifactId>
    <version>5.5.13</version>
</dependency>

Read the PDF and apply a watermark using PdfContentByte :

PdfReader reader = new PdfReader("original.pdf");
PdfStamper stamper = new PdfStamper(reader, new FileOutputStream("output.pdf"));
int pageCount = reader.getNumberOfPages();
for (int i = 1; i <= pageCount; i++) {
    PdfContentByte cb = stamper.getUnderContent(i);
    cb.beginText();
    cb.setFontAndSize(BaseFont.createFont(), 36f);
    cb.setColorFill(BaseColor.LIGHT_GRAY);
    cb.showTextAligned(Element.ALIGN_CENTER, "Watermark", 300, 400, 45);
    cb.endText();
}
stamper.close();
reader.close();

Method 3: Ghostscript (Command Line)

Ghostscript can add watermarks via a single command. After installing Ghostscript, run:

gs -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sOutputFile=output.pdf -c "newpath /Helvetica-Bold findfont 36 scalefont setfont 0.5 setgray 200 200 moveto (Watermark) show showpage" original.pdf

The command writes the watermark directly onto each page of original.pdf and produces output.pdf .

Method 4: Free Spire.PDF for Java

Free Spire.PDF is a free Java PDF library. Add its Maven dependency:

<dependency>
    <groupId>e-iceblue</groupId>
    <artifactId>free-spire-pdf-for-java</artifactId>
    <version>1.9.6</version>
</dependency>

Load the PDF, create a PdfWatermark , and add it to each page:

PdfDocument pdf = new PdfDocument();
pdf.loadFromFile("original.pdf");
for (int i = 0; i < pdf.getPages().getCount(); i++) {
    PdfPageBase page = pdf.getPages().get(i);
    PdfWatermark wm = new PdfWatermark("Watermark");
    wm.setFont(new PdfFont(PdfFontFamily.Helvetica, 36));
    wm.setOpacity(0.5f);
    page.getWatermarks().add(wm);
}
pdf.saveToFile("output.pdf");
pdf.close();

Method 5: Aspose.PDF for Java (Spring Boot Integration)

Aspose.PDF provides powerful PDF manipulation. Add the dependency:

<dependency>
    <groupId>com.aspose</groupId>
    <artifactId>aspose-pdf</artifactId>
    <version>21.4</version>
</dependency>

Expose two REST endpoints to add text or image watermarks:

@PostMapping("/addTextWatermark")
public ResponseEntity
addTextWatermark(@RequestParam("file") MultipartFile file) throws IOException {
    Document pdf = new Document(file.getInputStream());
    TextStamp ts = new TextStamp("Watermark");
    ts.setWordWrap(true);
    ts.setVerticalAlignment(VerticalAlignment.Center);
    ts.setHorizontalAlignment(HorizontalAlignment.Center);
    pdf.getPages().get_Item(1).addStamp(ts);
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    pdf.save(out);
    return ResponseEntity.ok()
        .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"watermarked.pdf\"")
        .contentType(MediaType.APPLICATION_PDF)
        .body(out.toByteArray());
}

@PostMapping("/addImageWatermark")
public ResponseEntity
addImageWatermark(@RequestParam("file") MultipartFile file) throws IOException {
    Document pdf = new Document(file.getInputStream());
    ImageStamp is = new ImageStamp("watermark.png");
    is.setWidth(100);
    is.setHeight(100);
    is.setVerticalAlignment(VerticalAlignment.Center);
    is.setHorizontalAlignment(HorizontalAlignment.Center);
    pdf.getPages().get_Item(1).addStamp(is);
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    pdf.save(out);
    return ResponseEntity.ok()
        .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"watermarked.pdf\"")
        .contentType(MediaType.APPLICATION_PDF)
        .body(out.toByteArray());
}

These endpoints can be tested with tools like Postman by sending a multipart/form‑data request containing the PDF file.

Conclusion

The article presents five practical ways to add watermarks to PDFs in a Spring Boot project: using Apache PDFBox, iText, Ghostscript, Free Spire.PDF, and Aspose.PDF. Choose the approach that best fits your project requirements and be sure to back up original files before overwriting them.