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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 Size Compression Level Expected Result Typical Output
50 MB Low ~10-30% 35-45 MB
50 MB Medium ~30-60% 20-35 MB
50 MB High ~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!