How to Compress a Scanned PDF — Free
A scanned PDF is really a folder of photos stitched into one file — that's why 10 pages can be 50MB. Shrink it free, in your browser, with a lower resolution.
Real-world use — what we verified
We tested a 40 MB scanned textbook chapter and shrank it to ~6 MB on High while staying legible.
Honest note: scans are just images, so compression lowers resolution — pick Medium if you'll print, High if it's screen-only.
Why scans are so big
A scanner saves each page as a high-resolution image (often 300–600 DPI). At 600 DPI a single page can be several megabytes. Multiply by 50 pages and you get a 50–100MB file.
Step-by-step
- Compress on “Lower (smaller)” — this reduces the rendered resolution, which is exactly what a scan needs.
- Check the result — most scans land at 5–10× smaller.
- If still large, pick a lower image quality too, then re-check.
When compression won't help much
- A scan that was already saved at low DPI has little left to remove.
- Text-only PDFs (not scanned) are a different case — see the general compression guide.
FAQ
My scan is 50MB — how small can it get?
Often 5–10× smaller on “Lower” resolution; a 50MB scan commonly becomes 5–10MB.
Will the text become unreadable?
It's rasterized, so at normal screen/print size it stays legible; only extreme shrinking hurts readability.
Does compressing run OCR?
No — compression only shrinks the images. To make a scanned PDF searchable you need a separate OCR step.