PDFs get big for two reasons: high-resolution embedded images and unnecessary metadata. Text takes almost no space at all. That means how much you can shrink a PDF depends heavily on what's in it — a text-only report might barely change, while a photo-heavy scan can shrink 80% with no visible loss.
How compression actually works
Under the hood, PDF compression re-encodes images at a lower resolution or with lossy JPEG compression, and drops metadata that isn't needed to display the file. Text in a real PDF is stored as characters, not images, so it stays crisp regardless of compression level.
Picking a level
Light — image quality preserved near-original. Use for archival scans and any file where visual fidelity matters. Typical reduction: 10-30%.
Medium — the default. Balanced setting; images look nearly identical to the eye. Typical reduction: 30-60%.
High — smallest file. Images become noticeably softer, especially photos. Use only when file size is a hard cap. Typical reduction: 50-80%.
Step-by-step
1. Open /compress-pdf.
2. Upload the PDF.
3. Pick Light, Medium or High.
4. Press Compress. The result downloads with a toast showing the size saved.
5. Open the compressed PDF and check the images at 100% zoom. Not happy? Try a lower level.
When compression barely changes anything
If your PDF is already mostly text, there's not much to compress. Also, some PDFs have already been compressed by the source software — running Compress again won't shrink them meaningfully.
Alternatives when compression isn't enough
The right compression setting depends on the content. Start with Medium; step up to High only if you must, and step down to Light for anything you'll archive.