Compress PDF
Reduce the size of PDFs full of photos or scans by re-encoding their images. See the before and after size instantly. Your file stays on your device.
Files never leave your deviceHow to compress a PDF
- Drop your PDF onto the box above.
- Drag the size slider to the size you need, or type an exact limit in KB. The estimate under it tells you straight away what that will take: re-compressing the images (text stays selectable) or turning pages into pictures. To choose the settings yourself, pick Set quality: Image quality sets the JPEG quality used when images are re-encoded, and Image resolution limits the longest side of each picture.
- Press Compress PDF. When it finishes you see the size before and after, and the percentage saved.
- Download the smaller file. If the tool could not make it smaller, it tells you and gives your original back.
What the compressor changes
Most of the weight in a large PDF comes from pictures: scans, photos and screenshots. The tool finds the images that can safely be recompressed, which are the 8-bit RGB and grey ones without transparency masks, re-encodes them as JPEG at your chosen quality and, if you asked for it, scales them down. A replacement is only used when it is meaningfully smaller. Everything else is left byte for byte as it was: text, fonts, vector graphics, links, form fields and images in other formats.
Maximum compression is a different strategy. It renders every page to a picture and rebuilds the document from those pictures. This can shrink scans dramatically, but text can no longer be selected or searched, so use it only for documents that are already images.
Why nothing is uploaded
Everything happens inside your browser. A background worker rewrites the PDF while the page remains responsive, and the finished file is created in memory and offered as a download. No server ever sees the document, which matters for scanned IDs, contracts and medical letters. You can verify this in your browser’s Network tab, as the FAQ explains.
Getting the best result
- A PDF that is mostly text may already be tiny. In that case there is little to gain and the tool keeps the original.
- Scans made at very high resolution compress best. Try limiting the resolution to 1500 pixels before lowering the quality, as it usually looks better.
- Quality below 50 makes text inside scanned images fuzzy. If the document will be printed, stay at 70 or above.
- Files that were already optimised by another tool may not shrink further.
- Compression is not reversible. Keep your original file.
- Have a hard size limit? Compress PDF to 1 MB and to 500 KB find the settings for you.
- For a quick email attachment, the “Up to 1500 px” option at quality 60 often brings a phone scan from many megabytes down to a few hundred kilobytes.
Frequently asked questions
How does PDF compression work here?
Most PDF weight comes from embedded images. The tool finds them, re-encodes them as JPEG at your chosen quality and swaps in the smaller version only when it saves space. Text and vectors stay sharp.
Why did my PDF barely shrink?
PDFs that contain mostly text and vector graphics have little to compress. Try the "Maximum" mode, which turns every page into an image. It can be much smaller but text is no longer selectable.
Could the result be larger than the original?
No. If the tool cannot make the file smaller it gives you the original back and tells you so.
Are my files uploaded anywhere? How can I check?
No. The PDF compressor runs entirely in your browser using JavaScript and WebAssembly, so your files never leave your device. You can verify it: open your browser's DevTools (F12, or Cmd+Option+I on a Mac), switch to the Network tab, tick "Preserve log", clear the list and process a file. You will only see requests for this site's own static files, never one that carries your data. You can also turn on "Offline" in the Network tab (or disconnect from the internet) once the page has loaded, and the tool keeps working.
Does it work offline?
Yes. After your first visit a service worker saves the tool to your device, so it opens and works without a connection. Only advertising needs the internet; the processing never does.