x
Skip to main content

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 "[email protected]" \
  -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!