In short: Compressing a PDF reduces its file size, mainly by re-encoding large images at a lower resolution or quality; text-only PDFs are usually already small and shrink little.
About Compress PDF
Scanned documents and PDFs full of photos often weigh tens of megabytes, too much for email attachments or upload forms that cap files at 5 or 10 MB. This compressor renders each page with Mozilla’s PDF.js and re-encodes it as an optimized JPEG at the resolution you choose, which often cuts scanned files to a fraction of their size.
All processing happens in your browser, which matters for the kind of documents people usually need to shrink: ID scans, bank statements, medical letters and contracts. If the result is not smaller than the original — which can happen with text-only PDFs — the tool tells you and you can keep the original.
How to use Compress PDF
- Choose or drop the PDF you want to shrink.
- Pick a compression level. Recommended keeps documents readable at a fraction of the size.
- Optionally convert to grayscale for black-and-white documents — it saves more space.
- Press Compress PDF and download the result. The new size and savings are shown.
Examples
Multi-page color scans usually shrink dramatically on the Recommended setting — often to a fraction of the original — which gets them under typical 5–10 MB upload limits.
For letters and forms, tick Convert to grayscale and choose Strong. The text stays legible on screen while the file gets much smaller.
Frequently asked questions
Why is my text no longer selectable?
Each page is re-rendered as an image to achieve strong compression. Keep the original file if you need searchable text or form fields.
Why did my file not get smaller?
Text-only PDFs exported from Word or similar tools are already compact. Converting them to images can make them larger, in which case the tool recommends keeping the original.
Is it safe for confidential documents?
Yes. The file is processed locally in your browser and never uploaded.
How long does it take?
Roughly a fraction of a second per page on a modern computer. Very long documents take longer on phones.
Updated November 2026 · Free, no signup · How we build and test tools