Compress PDF
Reduce PDF file size by compressing images, optimizing structure, and removing unnecessary data.
Important: Compression is permanent. Always keep a backup of the original if you might need maximum quality later.
How to Use#
- Upload Your PDF - Select one or more PDFs
- Choose Compression Level - Select quality vs. size balance
- Configure Options - Enable grayscale, line art, etc. (optional)
- Compress - Process the files
- Download - Get your compressed PDFs
Options#
| Option | Description |
|---|---|
| Optimize Level (1-9) | Controls compression aggressiveness. Higher = smaller file, lower quality. Levels 1-3 are light, 4-5 are moderate, 6+ trigger additional compression passes |
| Expected Output Size | Set a target file size (e.g. 25MB). The tool adjusts compression within a bounded number of attempts; reaching the target is not guaranteed. |
| Grayscale | Convert all images to grayscale. Can significantly reduce size for color documents where color isn't needed |
| Linearize | Optimize PDF for fast web viewing - reorders the file so the first page loads before the entire file is downloaded |
| Normalize | Normalize internal PDF structure for better compatibility |
| Line Art | Convert images to high-contrast line art. Useful for documents with diagrams, sketches, or black-and-white illustrations |
| Line Art Threshold (0-100) | Controls sensitivity of line art conversion. Default: 55. Only used when Line Art is enabled |
| Line Art Edge Level (1-3) | Edge detection strength for line art. 1 = light, 3 = strong. Only used when Line Art is enabled |
What Happens at Each Level#
- Levels 1-3 - Basic optimization, preserves quality
- Levels 4-5 - Image recompression enabled, moderate quality reduction
- Levels 6+ - Aggressive compression with additional processing passes
- Levels 8+ - Uses Zopfli compression on supported systems for maximum reduction
API Usage#
bash
curl -X POST http://stirling-pdf:8080/api/v1/misc/compress-pdf \
-F "[email protected]" \
-F "optimizeLevel=5" \
-F "grayscale=false" \
-F "linearize=false" \
-F "lineArt=false" \
-o compressed.pdfWith target size:
bash
curl -X POST http://stirling-pdf:8080/api/v1/misc/compress-pdf \
-F "[email protected]" \
-F "expectedOutputSize=10MB" \
-o compressed.pdfSee API Documentation for complete endpoint reference.
Decompress PDF#
Automation / API
There is also an automation option that does the opposite: it fully expands a compressed PDF so its contents are readable as plain text, which is handy for troubleshooting or editing a PDF by hand (the file gets larger). It runs through automation rather than a tool in the web app - see the API reference.
