Optimize PDF Files in Java

Aspose.PDF for Java exposes optimization features through Document.optimize, optimizeResources, and OptimizationOptions.

Optimize a PDF with general document optimization

Use this example when you want Aspose.PDF to apply the built-in whole-document optimization routine.

  1. Open the source PDF Document.
  2. Call optimize() on the document.
  3. Save the optimized file and compare the original and output sizes.
public static void optimizePdf(Path inputFile, Path outputFile) throws Exception {
    try (Document document = new Document(inputFile.toString())) {
        document.optimize();
        document.save(outputFile.toString());
    }
    printFileSizes(inputFile, outputFile);
}

Reduce PDF size by optimizing resources

This example focuses on resource-level optimization without manually configuring individual options.

  1. Open the source PDF Document.
  2. Run optimizeResources() to optimize internal resources.
  3. Save the result and print the input and output file sizes.
public static void reduceSizePdf(Path inputFile, Path outputFile) throws Exception {
    try (Document document = new Document(inputFile.toString())) {
        document.optimizeResources();
        document.save(outputFile.toString());
    }
    printFileSizes(inputFile, outputFile);
}

Compress all images in a PDF

Use this approach when image-heavy documents need a smaller file size and some image quality reduction is acceptable.

  1. Open the source PDF Document.
  2. Create OptimizationOptions and enable image compression with the required quality level.
  3. Optimize the document resources with those settings.
  4. Save the optimized file and compare file sizes.
public static void shrinkingOrCompressingAllImages(Path inputFile, Path outputFile) throws Exception {
    try (Document document = new Document(inputFile.toString())) {
        OptimizationOptions optimizeOptions = new OptimizationOptions();
        optimizeOptions.getImageCompressionOptions().setCompressImages(true);
        optimizeOptions.getImageCompressionOptions().setImageQuality(50);
        document.optimizeResources(optimizeOptions);
        document.save(outputFile.toString());
    }
    printFileSizes(inputFile, outputFile);
}

Remove unused objects from a PDF

This example removes unused objects that may remain in the document structure after edits or merges.

  1. Open the source PDF Document.
  2. Create OptimizationOptions and enable removal of unused objects.
  3. Optimize the resources and save the updated file.
  4. Print the original and reduced file sizes.
public static void removingUnusedObjects(Path inputFile, Path outputFile) throws Exception {
    try (Document document = new Document(inputFile.toString())) {
        OptimizationOptions optimizeOptions = new OptimizationOptions();
        optimizeOptions.setRemoveUnusedObjects(true);
        document.optimizeResources(optimizeOptions);
        document.save(outputFile.toString());
    }
    printFileSizes(inputFile, outputFile);
}

Remove unused streams from a PDF

Use this approach when you want to discard stream data that is no longer referenced by the document.

  1. Open the source PDF Document.
  2. Configure OptimizationOptions to remove unused streams.
  3. Optimize the resources, save the output document, and compare file sizes.
public static void removingUnusedStreams(Path inputFile, Path outputFile) throws Exception {
    try (Document document = new Document(inputFile.toString())) {
        OptimizationOptions optimizeOptions = new OptimizationOptions();
        optimizeOptions.setRemoveUnusedStreams(true);
        document.optimizeResources(optimizeOptions);
        document.save(outputFile.toString());
    }
    printFileSizes(inputFile, outputFile);
}

This example deduplicates repeated streams so identical content can be stored only once.

  1. Open the source PDF Document.
  2. Create OptimizationOptions and enable duplicate stream linking.
  3. Optimize the resources, save the output document, and print the file sizes.
public static void linkingDuplicateStreams(Path inputFile, Path outputFile) throws Exception {
    try (Document document = new Document(inputFile.toString())) {
        OptimizationOptions optimizeOptions = new OptimizationOptions();
        optimizeOptions.setLinkDuplicateStreams(true);
        document.optimizeResources(optimizeOptions);
        document.save(outputFile.toString());
    }
    printFileSizes(inputFile, outputFile);
}

Unembed fonts from a PDF

Use this option when reducing file size is more important than keeping embedded font data in the output.

  1. Open the source PDF Document.
  2. Configure OptimizationOptions to unembed fonts.
  3. Optimize the resources, save the document, and compare file sizes.
public static void unembedFonts(Path inputFile, Path outputFile) throws Exception {
    try (Document document = new Document(inputFile.toString())) {
        OptimizationOptions optimizeOptions = new OptimizationOptions();
        optimizeOptions.setUnembedFonts(true);
        document.optimizeResources(optimizeOptions);
        document.save(outputFile.toString());
    }
    printFileSizes(inputFile, outputFile);
}

Flatten annotations in a PDF

This example converts annotations into static page content so they no longer remain interactive objects.

  1. Open the source PDF Document.
  2. Iterate through each Page and its Annotation collection.
  3. Flatten every annotation and save the updated document.
public static void flattenAnnotations(Path inputFile, Path outputFile) {
    try (Document document = new Document(inputFile.toString())) {
        for (Page page : document.getPages()) {
            for (Annotation annotation : page.getAnnotations()) {
                annotation.flatten();
            }
        }
        document.save(outputFile.toString());
    }
}

Flatten PDF form fields

Use this approach when fillable form fields should become fixed content before distribution or archiving.

  1. Open the source PDF Document.
  2. Check whether the document contains form widgets.
  3. Flatten each Field represented by a WidgetAnnotation.
  4. Save the output file and print the file sizes.
public static void flattenForms(Path inputFile, Path outputFile) throws Exception {
    try (Document document = new Document(inputFile.toString())) {
        if (document.getForm() != null && document.getForm().size() > 0) {
            for (WidgetAnnotation annotation : document.getForm()) {
                if (annotation instanceof Field field) {
                    field.flatten();
                }
            }
        }
        document.save(outputFile.toString());
    }
    printFileSizes(inputFile, outputFile);
}

Convert a PDF to grayscale

This example changes each page to grayscale, which can help reduce color complexity and standardize output for archival or printing workflows.

  1. Open the source PDF Document.
  2. Iterate through each Page in the document.
  3. Call makeGrayscale() on every page and save the output file.
public static void convertPdfFromRgbColorspaceToGrayscale(Path inputFile, Path outputFile) {
    try (Document document = new Document(inputFile.toString())) {
        for (Page page : document.getPages()) {
            page.makeGrayscale();
        }
        document.save(outputFile.toString());
    }
}

Use FlateDecode image compression

Use this pattern when you want to apply Flate-based compression to images during PDF resource optimization.

  1. Open the source PDF Document. «««< HEAD
  2. Create OptimizationOptions and set the image encoding to ImageEncoding.Flate. =======
  3. Create OptimizationOptions and set the image encoding to ‘ImageEncoding’.Flate.

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  1. Optimize the document resources and save the output file.
public static void usingFlatedecodeCompression(Path inputFile, Path outputFile) {
    try (Document document = new Document(inputFile.toString())) {
        OptimizationOptions optimizationOptions = new OptimizationOptions();
        optimizationOptions.getImageCompressionOptions().setEncoding(ImageEncoding.Flate);
        document.optimizeResources(optimizationOptions);
        document.save(outputFile.toString());
    }
}

This helper method reports the size difference between the source file and the optimized output file.

  1. Read the size of the input file.
  2. Read the size of the output file.
  3. Print both values in a single status message.
private static void printFileSizes(Path inputFile, Path outputFile) throws Exception {
    System.out.println("Original file size: " + Files.size(inputFile)
            + ". Reduced file size: " + Files.size(outputFile));
}
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