PDF Compressor
Compress PDF files to reduce file size online for free. Up to 80% reduction via image resampling. No upload to servers.
About This Tool
PDF Compressor reduces the file size of your PDF documents by optimizing images, removing redundant data, and streamlining internal structures. Shrink large PDFs for email, cloud storage, or faster web downloads while maintaining readable quality — essential for office professionals and anyone sharing documents online.
Drag & drop a PDF file here, or click to browse
Only PDF files are supported
How to Use
- Drag and drop a PDF file into the upload area above, or click to browse and select a file.
- Choose a compression level: High (maximum compression), Medium (standard), or Low (light optimization).
- Click the 'Compress PDF' button to start compression.
- Review the original size, compressed size, and compression ratio.
- Click the 'Download' button to save the compressed PDF.
Frequently Asked Questions
How does PDF compression work?
Each page is rendered as an image, then re-encoded at reduced quality and resolution based on your chosen compression level. Since images make up most of a PDF's file size, this approach is the most effective.
Will quality be affected?
It depends on the compression level. 'Low' shows barely noticeable difference (~30% reduction). 'Medium' has slight quality loss (~50% reduction). 'High' has visible quality reduction but achieves up to 70%+ reduction. Text readability is maintained at all levels.
Is it safe?
Yes, all processing happens entirely in your browser. Your files are never uploaded to any server, making it 100% private and secure.
Does it work on text-only PDFs?
Text-heavy PDFs are already small, so compression may be limited. This tool is most effective on PDFs containing images (scanned documents, photo-heavy reports, etc.).
What is the maximum file size?
It depends on your browser's available memory. Typically, you can handle PDF files up to 50MB without issues. Very large files may take longer to process.
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How It Works
The PDF is loaded as an ArrayBuffer through the File API and parsed using pdf-lib. The compression process works in several stages: embedded images are decoded, re-encoded at lower quality using Canvas toBlob(), and replaced in the PDF stream; duplicate font subsets and unused objects are identified and removed; and metadata streams are cleaned. The optimized PDF byte array is reassembled by pdf-lib's save() method with the useObjectStreams option enabled for additional size reduction. A before-and-after comparison shows exact bytes saved.
All parsing, image re-compression, and PDF reassembly happen entirely in your browser using pdf-lib, the Canvas API, and the File API. Your documents are never sent to any external server.