How to flatten PDF layers in Java (Tutorial)

TLDR;

Flattening PDF layers in Java is a way to lock a document’s appearance, ensure cross-device compatibility, and reduce file size by merging optional content into a single layer.

Using the JPedal library, the process involves three main steps:

1. Load: Initialize the PdfManipulator and load your PDF file.
2. Flatten: Call the .flattenLayers() method to merge the content.
3. Save: Use .apply() and .writeDocument() to export the final, simplified PDF.

What does it mean to flatten a PDF?

Flattening a PDF merges all of its separate interactive layers, like signatures and annotations into a single, non-editable visual layer. This locks the content in place, preventing any further changes and ensuring the document looks exactly the same on every device or printer.

Why would you flatten PDF layers?

A common reason for wanting to flatten layers is that it will preserve the document’s appearance across devices. PDF files with complicated visibility rules may expose bugs in different software implementations, so flattening the optional content removes this risk.

Additionally, a draft version of a document may use layers to experiment with different appearances or content. The document would then be flattened into the final version so that these draft layers would be removed. This also has the benefit of reducing the file size.

How to set up JPedal

To get started using the JPedal PDF library, download the JPedal trial jar from our website, and add it to your Java project.

How to flatten layers in a PDF in Java

By using the code snippet below you can flatten the target PDF. Using JPedal’s PDF Manipulator class:

1. Load the document,
2. Call the flattenLayers() method
3. Save the result

final PdfManipulator pdf = new PdfManipulator();

pdf.loadDocument(new File("inputFile.pdf"));


pdf.flattenLayers();


pdf.apply();

pdf.writeDocument(new File("outputFile.pdf"));

pdf.reset();

pdf.closeDocument();

Download JPedal

You can download a JPedal trial jar to see you it works.

Resources

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FAQs

//Convenience static method (see class for additional options)
ExtractClippedImages.writeAllClippedImagesToDir("inputFileOrDirectory", "outputDir", "outputImageFormat", new String[] {"imageHeightAsFloat", "subDirectoryForHeight"});

final PdfManipulator pdf = new PdfManipulator();
pdf.loadDocument(new File("inputFile.pdf"));
pdf.addPage(1, PaperSize.A4_LANDSCAPE);
pdf.addText(1, "Hello World", 10, 10, BaseFont.HelveticaBold, 12, 1, 0.3f, 0.2f);
pdf.addImage(1, new BufferedImage(), new float[] {0, 0, 100, 100});
pdf.rotatePage(1, 90);
pdf.apply();
pdf.writeDocument(new File("outputFile.pdf"));

Viewer viewer = new Viewer();
viewer.setupViewer();
viewer.executeCommand(ViewerCommands.OPENFILE, "pdfFile.pdf");

//Convenience static method (see class for additional options)
ExtractTextAsWordList.writeAllWordlistsToDir("inputFileOrDirectory", "outputDir", -1);

PdfMerge.mergeFiles(new File("inputFile1.pdf"), new File("inputFile2.pdf"), new File("outputFile.pdf"));

PdfManipulator.splitInHalf(new File("inputFile.pdf"), new File("outputFolder"), pageToSplitAt);

PrintPdfPages print = new PrintPdfPages("C:/pdfs/mypdf.pdf");

if (print.openPDFFile()) {
    print.printAllPages("Printer Name");
}

//Convenience static method (see class for additional options)
ExtractClippedImages.writeAllClippedImagesToDir("inputFileOrDirectory", "outputDir", "outputImageFormat", new String[] {"imageHeightAsFloat", "subDirectoryForHeight"});

//Convenience static method (see class for additional options)
ArrayList resultsForPages = FindTextInRectangle.findTextOnAllPages("/path/to/file.pdf", "textToFind");

java -jar jpedal.jar --inspect "inputFile.pdf"

PdfSigner.signPdf(
        "inputFile.pdf",
        "outputFile.pdf",
        "keystorePassword",
        "keystoreFile.p12",
        "signerName",
        "signerLocation",
        "signingReason",
        ACCESS_PERMISSION.P1
);