Compress PDF — Reduce PDF File Size

What it does

Use it when an email or an upload form says your PDF is too large. Most of a PDF’s weight is the photos and scanned images inside it. This tool takes those images one by one, recompresses them as JPEG, scales down the oversized ones, and puts them back in the same place. Text, tables, shapes, links and bookmarks are not touched, so the document keeps its structure and only the size goes down. Photos do lose a little quality, and colours can shift very slightly. Everything happens in your browser.

How to use

1. Drop one PDF on the dashed area or press Choose PDF.
2. Pick a method. Recompress images only is right for most files.
3. Pick a goal:
   • Quality level: light, balanced or strong.
   • Target size: a size in MB such as 2 or 9.5; the best quality that fits is chosen for you.
4. Press Compress PDF to see the original and new size, the change in percent and a first-page preview of both.
5. Download the result if you are happy with it.

How it works

• Quality levels: light keeps images up to 2400 px on the long side at JPEG quality 85%, balanced 1600 px at 72%, strong 1000 px at 55%. Smaller images keep their size and only get the new quality.
• When an image is replaced: only when the new version is at least 5% smaller, so images that are already small do not lose quality.
• Images left alone: transparency masks and the images that use them as masks are kept lossless; CMYK, palette and spot-colour images, JPEG 2000, JBIG2 and CCITT data, images that are not 8 bits per channel, images under 64×64 px or 8 KB, and very large images over 25 megapixels (about 16.7 megapixels on iPhone and iPad) are not changed; a large image has to be unpacked in memory all at once, so it is skipped to keep the tab from freezing. Grayscale images become RGB JPEGs and images with an ICC colour profile become plain RGB, so colours can shift very slightly.
• Turn every page into an image: each page is drawn by PDF.js into one JPEG. Text selection, search, links and form fields are lost, but scans shrink a lot.
• Where it runs: image recompression runs in a separate browser thread (a Web Worker), so the page stays responsive while it works.
• Limits: files up to 100 MB. PDFs that need a password to open, or that carry editing restrictions, cannot be processed.
• Libraries: pdf-lib (MIT) edits the PDF, fflate (MIT) unpacks compressed image data and PDF.js (Apache-2.0) renders previews and pages. Ghostscript is not used.

Examples

Situation	Suggested setting	What to expect
Report with phone photos	Images only, balanced	The more photos, the bigger the saving
Portfolio for a 10 MB upload limit	Target size 9.5	Best quality that stays under 10 MB
Contract scanned in colour	Images only, strong; if not enough, every page as an image	A few hundred KB per page
Text document from Word	—	Already small, barely changes

If the file is still over a limit, Split PDF by Size can cut it into several files.