Скачать или смотреть Adding a Watermark to PDFs using Apache PDFBox

Learn how to properly add a watermark to your PDF files using Apache PDFBox, including overlays and transparent images, while retaining original content.
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How to Add a Watermark to PDF Files with Apache PDFBox

If you are working with PDF files and need to add a watermark, you may encounter challenges that lead to the original content being hidden or replaced. This article will guide you through two effective methods of adding watermarks using Apache PDFBox while ensuring the original contents remain clearly visible.

Understanding the Problem

When adding a watermark to an existing PDF using library tools such as Apache PDFBox, you have different options:

Using an Overlay PDF: You can overlay a separate PDF that contains your watermark.

Adding a Transparent Image: Alternatively, you can add a transparent image as the watermark.

However, many developers find that both methods may obscure the original content of the PDF. This article will explain how you can resolve this issue effectively.

Methods to Add Watermarks

Method #1: Adding Overlay PDF

This method allows you to overlay another PDF on top of the original. Here’s how you can implement it:

[[See Video to Reveal this Text or Code Snippet]]

Method #2: Adding Transparent Image

In this method, you add a transparent image that serves as the watermark. Usually, when you use the following code, the original content may get covered:

[[See Video to Reveal this Text or Code Snippet]]

Key Issues with Original Methods

The main issue arises when the PDPageContentStream is used, which replaces the current page content instead of appending to it. As a result, the original contents do not show up.

Solution: Correctly Appending Content

To resolve this issue and ensure that your watermark doesn’t cover the existing content, you should modify how you construct the PDPageContentStream:

[[See Video to Reveal this Text or Code Snippet]]

This approach allows you to append new content on top of the existing page instead of replacing it, allowing both the watermark and original content to coexist visibly.

Conclusion

Adding a watermark to PDFs using Apache PDFBox involves understanding how to manage content streams effectively. By using overlay PDFs and transparent images correctly, and ensuring the append mode is utilized for your content streams, you can create visually appealing PDF documents without losing original content.

Test Cases

Here are the two testing methods you can use to apply and verify your watermark:

Overlay PDF Test: Validate that the overlay pdf displays correctly without obscuring original text.

Image Watermark Test: Ensure your transparent image appears correctly with the desired alpha value.

By following these guidelines, you can confidently add watermarks to your PDFs using Apache PDFBox while keeping your content intact. Happy coding!