Compress PDF PDF
Shrink a heavy PDF by re-rendering its pages at a lower resolution.
Compress PDF is a free online tool that shrink a heavy PDF by re-rendering its pages at a lower resolution. It runs entirely in your web browser using pdf-lib and pdf.js and Canvas 2D, so files are processed on your own device and never uploaded to a server. There is no sign-up, no file size limit imposed by the site, no watermark and no paid tier.
- Price
- Free — no account, no quota, no watermark
- Category
- Where it runs
- In your browser, on your device
- Files uploaded
- None
- Technology
- pdf-lib, pdf.js, Canvas 2D
- Settings
- 3
- Works offline
- Yes, after the first visit
About Compress PDF
This is a rasterizing compressor: it renders every page to an image and rebuilds the PDF from JPEGs. That is brutally effective on scans and image-heavy documents — 70–90% reductions are normal — and useless on a text-only PDF that is already small. The trade-off is real and worth understanding before you use it.
How to use it
- Choose a file, or drag it onto the drop zone.
- Set page resolution, jpeg quality and convert to grayscale.
- Press "Compress PDF", then download what comes back.
The 3 settings
| Setting | What it does | Default |
|---|---|---|
| Page resolution | Choose from 3: Low — smallest file, Medium — balanced, High — best quality. | Medium — balanced |
| JPEG quality | Range 20–95%. | 70% |
| Convert to grayscale | On or off. Off by default. | Off |
Under the hood
| Runs on | pdf-lib — builds and rewrites the PDF structure; pdf.js — renders and reads existing PDF pages; Canvas 2D — does the pixel work |
| Controls | Page resolution, JPEG quality, Convert to grayscale |
Questions
Will the text still be selectable after compressing?
No. This method replaces the text layer with a picture of the text, so the result is not selectable, searchable or screen-reader accessible. If those matter, do not use this tool — send the original instead.
Why did my PDF get bigger instead of smaller?
Because it was already efficient. A 200KB text-only PDF has almost no image data to squeeze, so turning it into page images adds weight. The tool tells you when this happens rather than handing you a worse file quietly.
Which settings should I use for a scanned document?
Medium resolution at 60–70% quality is the sweet spot for scanned text, and ticking grayscale often halves the size again with no readability loss. Drop to low resolution only if the file still needs to be smaller.
How small can I get a file for an email attachment?
Most 25MB scans land under 3MB at medium/70%. If you need to hit a hard limit, lower the JPEG quality first — it costs less visible detail than dropping the resolution.