Free Online PDF Compressor — No Upload Required
Most online PDF compressors require you to upload your file to a remote server, where it's processed and sent back. This raises serious privacy concerns, especially for sensitive documents like contracts, tax returns, medical records, or financial statements.
Our PDF compressor is fundamentally different. It uses open-source JavaScript libraries to render and re-compress your PDF pages directly inside your web browser. Your PDF file never leaves your computer — not even for a millisecond.
How PDF Compression Works
PDF files often contain high-resolution images, embedded fonts, metadata, and redundant data structures that inflate the file size far beyond what's necessary. Our compressor applies several techniques to reduce file size:
- Page rendering: Each page is rendered at the target resolution (72–300 DPI depending on your chosen quality level) using the browser's canvas engine.
- JPEG recompression: Rendered pages are re-encoded as JPEG images with quality settings matched to your compression level, dramatically reducing file size.
- PDF reassembly: Compressed page images are assembled into a new, optimised PDF document with correct page dimensions.
Compression Levels Explained
| Level | DPI | Typical Reduction | Best For |
|---|---|---|---|
| Maximum (screen) | 72 | 60–70% | Email attachments, web viewing |
| Balanced (ebook) | 150 | 40–50% | General sharing, on-screen reading |
| High Quality (printer) | 300 | 20–30% | Home and office printing |
| Minimal (prepress) | 300 | 10–15% | Professional printing, colour-critical work |
Privacy & Security
Because all processing happens in your browser using JavaScript, your files enjoy the strongest possible privacy guarantee: zero server contact. This makes our tool suitable for compressing confidential documents, legal contracts, medical records, and any file you wouldn't want to upload to a third-party server.
Technical Details
This tool is powered by PDF.js (Apache-2.0) for PDF rendering and pdf-lib (MIT) for PDF assembly. Each page is rendered at the target resolution, re-compressed as JPEG, and assembled into a new PDF — all within your browser. The libraries are loaded on first use (~2 MB) and cached for subsequent uses.
Browser requirements: Chrome 69+, Firefox 105+, Safari 16.4+, or Edge 79+ (any modern browser with OffscreenCanvas and Web Worker support).
This tool is provided for convenience. Compression renders pages as images, which produces excellent results for scanned documents and image-heavy PDFs. Always verify compressed PDFs before deleting the originals.