A report with photos lost 19 to 32% of its size here; a text-only file barely changed. That is the pattern: most of a large PDF is usually its photos, and this tool recompresses those photos and, at the balanced and strong levels, scales down any that are bigger than a screen needs. Text, fonts and drawings stay exactly as they were.
Three examples
| Light | Balanced | Strong | |
|---|---|---|---|
| A 2-page report with two photos, 560 KB | 453 KB (−19%) | 405 KB (−28%) | 379 KB (−32%) |
| A one-page text-only letter, 19.9 KB | 17.7 KB (−11%) | 17.7 KB (−11%) | 17.7 KB (−11%) |
| A 3-page statement with one photo stored without loss, 651 KB | unchanged | unchanged | unchanged |
In the report, only the space photo was stored as JPEG; the second photo was stored without loss and was left alone, which is why Strong saved 32% and not more. The letter shrank a little only because it was saved more compactly; there were no photos to work on. In the statement the only photo was stored without loss, which the tool leaves alone, so nothing could be gained, so the tool said so and kept the original instead of handing back the same file under a new name.
The three levels
| Level | Photos | Good for |
|---|---|---|
| Light | Original pixel size, JPEG quality 80 | Printing, archiving |
| Balanced | Up to 2000 px on the long side, quality 70 | Email, most upload forms |
| Strong | Up to 1400 px on the long side, quality 55 | Strict size limits |
We would pick Balanced for email: photos at 2000 px still fill a laptop screen, and that is all an email attachment needs. Go to Strong only if you are still over a limit, and check that small print in photographed pages is still readable.
What it leaves alone
Screenshots, diagrams and scans stored without JPEG compression, and CMYK print images, are not converted: turning them into JPEG would blur lines and text or shift colors. Password-protected PDFs cannot be compressed here; save a copy without the password first. The work is done by pdf-lib and the MozJPEG encoder in a background thread, and a recompressed photo replaces the original only when it is at least 10% smaller.