How to use Compress PDF
- Choose the PDF you want to make smaller.
- Pick a level: Light keeps the most detail, Strong makes the smallest file.
- Select Compress PDF. The images are re-encoded in your browser.
- Check the before and after sizes, then download.
How the compression works
Most of a large PDF's size is images: scanned pages and photos stored at a higher resolution than anyone needs on screen. The tool finds each JPEG image in the file, decodes it with your browser's own image codec, scales it so its long side is at most 2,400, 1,800 or 1,300 pixels depending on the level, and encodes it again at a lower JPEG quality.
Each new image only replaces the old one if it is actually smaller. Text, fonts and vector drawings are left exactly as they were, so text stays sharp and selectable however strong the setting. If the finished file would not be smaller than your original, you get your original back unchanged, and the page tells you why.
Choosing a level
Light keeps images at about 200 dpi on a full A4 page, which still prints well. Balanced, the default, is about 150 dpi: sharp on any screen and fine for most printing. Strong goes to about 110 dpi with heavier JPEG compression, for email attachments and upload limits where size matters more than detail.
After each run you see the real sizes before and after, and how many images were re-encoded. Compare that with tools that only re-save the file and report a 0% saving on a scanned document.
What happens to your file
The PDF is read into this browser tab and processed in a background worker. Images are decoded and re-encoded by the browser itself, not by a server, and nothing is uploaded. Images in print colour formats (CMYK), masked images and unusual formats are skipped rather than risk changing their colours, and the result tells you how many were skipped.
Common uses
Getting a scanned contract under an email attachment limit, shrinking a photo-heavy report before uploading it to a portal with a size cap, or making a scanned book small enough to read on a phone. If one part of a document is much heavier than the rest, split it, compress that part, and merge it back.
Questions
- Why didn't my PDF get smaller?
- PDF size usually comes from photos and scans. If a file is mostly text and fonts, or its images are already compact, there is little to remove, and the tool tells you so and gives back your original instead of a bigger file.
- Will the text get blurry?
- No. Only images are re-encoded. Text, vector drawings and fonts are not touched, so text stays sharp and selectable.
- Is my PDF uploaded?
- No. The images are decoded and re-encoded by your browser's own image codecs, in a background worker in this tab. Nothing is sent to a server.
- Which images are compressed?
- Colour and greyscale JPEG images, which covers most photos and scans. Images in print colour formats (CMYK), masked images and other formats are left exactly as they are, and the result tells you how many.