How this compression works
Most of a large PDF's size comes from photos and scanned pages stored inside it. The compressor downsamples oversized images to a sensible resolution and re-encodes them efficiently, replacing an image only when the new version is clearly smaller. It also compresses uncompressed internal data losslessly and removes leftover objects from earlier edits.
Text, fonts, and vector artwork are never converted to images, so the document stays searchable, selectable, and crisp at any zoom.
- Light — images up to 2800 px, high quality: barely visible changes
- Balanced — images up to 2000 px: clear on screen and in print at normal sizes
- Strong — images up to 1400 px: smallest files, for scans and photo-heavy reports
When a PDF won't get smaller
Text-only PDFs and files that were already optimized have little to remove. If a result isn't at least 3% smaller, the tool tells you and recommends keeping your original instead of offering a file that's no better.
Getting a PDF under a limit like 1 MB? Start with Balanced; if it's still too big, try Strong. Very long scanned documents may need to be split or rescanned at a lower resolution.