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Version: 2.0 (Beta)

Compress PDF

Tool ID: compress-pdf

Reduce PDF file size while maintaining acceptable quality for your needs. Stirling-PDF's compression tool optimizes images, removes unnecessary data, and applies various compression techniques to significantly reduce file sizes.

What is PDF Compression?​

PDF compression reduces file size by:

  • Compressing embedded images
  • Removing duplicate resources
  • Optimizing fonts and content streams
  • Removing unused or redundant data
  • Downsampling high-resolution images

Important: Compression is permanent. Always keep a backup of the original if you might need maximum quality later.

How to Use Compress​

  1. Upload Your PDF - Select one or more PDFs to compress
  2. Choose Compression Level - Select quality vs. size balance
  3. Configure Options - Adjust advanced settings (optional)
  4. Compress - Process the files
  5. Download - Get your compressed PDFs

Compression Levels​

Low Compression​

  • Size Reduction: ~10-30%
  • Quality: Excellent - minimal quality loss
  • Best For:
    • Documents with important images
    • Professional presentations
    • Photos that need high quality
    • Documents for printing

Use When: You need smaller files but can't compromise on quality.

  • Size Reduction: ~30-60%
  • Quality: Good - balanced quality/size tradeoff
  • Best For:
    • General documents
    • Email attachments
    • Web publishing
    • Most use cases

Use When: You want good file size reduction with acceptable quality.

High Compression​

  • Size Reduction: ~60-90%
  • Quality: Fair - noticeable quality reduction
  • Best For:
    • Text-heavy documents
    • Documents with simple graphics
    • Archival storage where quality is secondary
    • Very large documents that must be smaller

Use When: File size is critical and quality is less important.

Custom Compression​

  • Manual Control: Set exact compression parameters
  • Advanced Users: Fine-tune image DPI, quality, color depth
  • Testing: Experiment to find optimal settings

Compression Options​

Image Quality​

Image DPI (Resolution):

  • 300 DPI - High quality, suitable for printing
  • 150 DPI - Standard quality, good for screen viewing
  • 72 DPI - Low quality, very small files

Image Quality Percentage:

  • 90-100% - Minimal compression, excellent quality
  • 70-90% - Balanced compression (recommended)
  • 50-70% - Aggressive compression, visible artifacts

Color Depth​

Options:

  • Full Color (24-bit) - All colors preserved
  • Grayscale (8-bit) - Convert to black/white shades
  • Monochrome (1-bit) - Pure black and white only

Tip: Convert color documents to grayscale if color isn't needed - can reduce size by 50%+.

Advanced Options​

Optimize Images:

  • Compress and optimize all embedded images
  • Downsample high-resolution images
  • Remove image metadata

Remove Duplicate Resources:

  • Detect and remove duplicate images/fonts
  • Significant savings for documents with repeated elements

Compress Content Streams:

  • Apply advanced compression to PDF content
  • Optimize internal PDF structure

Remove Unused Objects:

  • Clean up leftover objects from editing
  • Remove orphaned resources

What Gets Compressed?​

Images​

  • JPEG images re-compressed at lower quality
  • PNG images optimized and potentially converted
  • High-resolution images downsampled
  • Duplicate images removed

Fonts​

  • Subset fonts (include only used characters)
  • Remove unused font data
  • Optimize font embedding

Content​

  • Compress content streams with ZLIB/DEFLATE
  • Optimize PDF structure
  • Remove redundant data

Metadata​

  • Optionally remove or reduce metadata
  • Remove thumbnail previews
  • Strip editing history

Tips & Best Practices​

Before Compressing​

  1. Keep a backup - Compression is permanent
  2. Test on a copy - Try different settings first
  3. Check file size - Already compressed? May not reduce much
  4. Identify content type - Text vs. images requires different approaches

Choosing Compression Level​

For Text-Heavy Documents:

  • ✅ High compression works well
  • ✅ Text quality remains excellent
  • ✅ 70-90% size reduction common

For Image-Heavy Documents:

  • ⚠️ Start with medium compression
  • ⚠️ Test before applying to batch
  • ⚠️ 30-60% size reduction typical

For Mixed Content:

  • ✅ Medium compression (recommended)
  • ✅ Test on sample pages
  • ✅ 40-70% size reduction expected

After Compressing​

  1. Verify quality - Open and review compressed PDF
  2. Check images - Zoom in on important images
  3. Test printing - If document will be printed
  4. Compare file sizes - Ensure compression worked

Common Issues​

"File not compressing much"​

Possible Causes:

  • PDF already compressed
  • Mostly text with few images
  • Images already optimized

Solutions:

  • Try higher compression level
  • Check if file is already compressed
  • Some PDFs have minimal compression potential

"Quality too poor after compression"​

Possible Causes:

  • Compression level too high
  • Source images low quality
  • DPI set too low

Solutions:

  • Reduce compression level
  • Increase image DPI setting
  • Use "Medium" or "Low" compression
  • Keep original for high-quality needs

"Compression failed"​

Possible Causes:

  • Corrupted PDF
  • Encrypted/password-protected PDF
  • Unusual PDF structure

Solutions:

  • Try repairing PDF first
  • Remove password protection
  • Try different compression settings

Batch Compression​

Compress multiple PDFs at once with consistent settings:

  1. Upload Multiple Files - Select multiple PDFs
  2. Choose Settings - Apply same settings to all
  3. Process Batch - Compress all files
  4. Download ZIP - Get all compressed PDFs in one archive

Tip: Test settings on one file first, then apply to batch.

Compression vs. File Size​

Expected Results​

Original SizeCompression LevelExpected ResultTypical Output
50 MBLow~10-30%35-45 MB
50 MBMedium~30-60%20-35 MB
50 MBHigh~60-90%5-20 MB

Note: Actual results vary based on content type (text vs. images) and whether file is already compressed.

Document Type Comparison​

Scanned Documents (Image-heavy):

  • Excellent compression potential
  • 60-90% reduction common with high compression
  • Most benefit from compression

Digital PDFs (Text-heavy):

  • Moderate compression potential
  • 20-40% reduction typical
  • Already relatively small

Mixed Content:

  • Good compression potential
  • 40-70% reduction expected
  • Varies by image/text ratio

Technical Details​

Compression Methods​

Stirling-PDF uses multiple compression techniques:

Image Compression:

  • JPEG compression for photos
  • FLATE compression for graphics
  • Downsampling for high-resolution images

Content Stream Compression:

  • ZLIB/DEFLATE algorithms
  • Object stream compression
  • Cross-reference stream compression

Structure Optimization:

  • Remove unused objects
  • Deduplicate resources
  • Optimize PDF structure

Processing Engine​

Uses Apache PDFBox and ImageMagick for compression:

  • Industry-standard tools
  • Proven reliability
  • Wide format support

Use with Other Tools​

Common Workflows​

Scan → OCR → Compress

  1. Scan documents to PDF
  2. OCR to make searchable
  3. Compress to reduce file size

Merge → Compress

  1. Merge multiple PDFs
  2. Compress combined document
  3. Share smaller file

Convert → Compress

  1. Convert images to PDF
  2. Compress to optimize size
  3. Email or upload

Edit → Compress → Archive

  1. Edit and modify PDFs
  2. Compress for storage
  3. Archive with smaller footprint

API Usage​

Compress PDFs programmatically via API:

curl -X POST http://stirling-pdf:8080/api/v1/compress/pdf \
  -F "fileInput=@document.pdf" \
  -F "optimizeLevel=2" \
  -F "imageQuality=70" \
  -F "imageDpi=150" \
  -o compressed.pdf

Parameters:

  • optimizeLevel - 0 (low), 1 (medium), 2 (high)
  • imageQuality - 1-100 (percentage)
  • imageDpi - Target DPI for images
  • fastWebView - Optimize for web streaming

See API Documentation for complete endpoint reference.

  • OCR - Make searchable before compressing
  • Convert - Convert formats before compressing
  • Multi-Tool - Chain compression with other operations
  • Merge - Combine then compress

Summary​

Stirling-PDF's Compress tool provides:

✅ Significant size reduction - 10-90% smaller files ✅ Quality control - Choose your size/quality balance ✅ Batch processing - Compress multiple files at once ✅ Smart optimization - Multiple compression techniques ✅ Flexible options - Fine-tune for your needs ✅ API access - Automate compression workflows

Perfect for reducing email attachment sizes, optimizing storage, and speeding up file transfers!