Compress PDF

How to Compress PDF

1. Press Choose a PDF, or drop your file on the box above.
2. Under How small?, pick Best quality, Balanced, Small or Smallest. Or pick Fit a size and type the limit in KB.
3. Press Compress PDF and wait for the bar to fill.
4. Check the old and new size, then press Download. Your original file is not changed.

What gets smaller, and what can’t

Compress PDF works on the pictures inside your file: photos, scanned pages and images pasted into a document. Each picture is saved again as a JPEG with fewer pixels and a lower quality. Text, fonts, lines and drawings are not touched, so words stay sharp and can still be selected and searched.

After the pictures, the whole file is rewritten with the strongest lossless packing for everything else. That removes some waste, but text and drawings are already compact and cannot shrink much. So a scanned document or a photo-heavy brochure can get much smaller, while a PDF made straight from Word or Excel often shrinks only a little.

A picture is only replaced when the new version is at least 10% smaller. Some pictures are left exactly as they are: small ones under about 20 KB such as logos and icons, pictures stored in print colours (CMYK), pure black-and-white scans (one bit per dot, including fax-style formats) that are already very compact, and a few other special formats. If your file is mostly made of these, expect little change. Colour pictures stay in colour: there is no black-and-white or grayscale option.

The four levels

Each level sets the most pixels a picture may keep on its longest side, and the JPEG quality. A picture that is already smaller than the limit is not enlarged. For a picture that fills a whole A4 page, the pixel limit works out to roughly the pixels per inch shown below.

Start with Balanced. If the result is still too big, try Small, then Smallest. If you have a number to meet, use Fit a size instead and let the tool choose. At Small and Smallest, zoom in on the result and check that small print can still be read before you send it.

• Best quality: up to 2400 pixels, JPEG quality 82%. About 200 pixels per inch on a full A4 page. For files you will print or zoom into.
• Balanced (selected at the start): up to 1800 pixels, quality 70%. About 150 pixels per inch. Good for reading on screen and for most forms.
• Small: up to 1300 pixels, quality 55%. About 110 pixels per inch.
• Smallest: up to 900 pixels, quality 40%. About 75 pixels per inch. For the strictest limits.

Fit a size: when a form has an upload limit

Choose Fit a size and type the limit in the box Must be under (KB). The tool tries the levels in order, Best quality first, then Balanced, Small and Smallest, and keeps the first result that fits. So you get the best quality of the four that is under your number. Because it may need four tries, a big file can take longer than with a single level. It all runs on your own device, so nothing is uploaded while you wait.

If even Smallest is still over your number, you get the smallest file it could make, with the message “The smallest we could reach is …”. You can still download it, and it is smaller than your original, but it will not pass that limit. At Smallest the pictures are already as light as this tool makes them, so the rest can only shrink by keeping fewer pages or starting from smaller pictures.

You never get a bigger file. If nothing could be made smaller, you see “This PDF is already as small as it can be made” and no new file is made.

Typing the right number

Upload forms and portals often set limits such as 100 KB, 200 KB, 500 KB, 1 MB or 2 MB. Only the rule printed on the form you are filling in counts, so read it there. Some forms give a range, with a minimum as well as a maximum.

Here 1 KB is 1,024 bytes and 1 MB is 1,024 KB. Some websites count 1 KB as 1,000 bytes, so a file just under our 100 KB can be slightly over theirs. To be safe, type a little less than the limit: 95 for 100 KB, 190 for 200 KB, 475 for 500 KB, 950 for 1 MB and 1900 for 2 MB.

This tool only makes files smaller. If a form also asks for a minimum size, it cannot make your PDF bigger to reach it.

If the file is still too big, or won’t open

• Drop pages the form doesn’t need: in Split PDF, take out only the pages you want, then compress that file.
• If the form accepts more than one file, split the PDF into parts and upload each part.
• If the form takes pictures instead of a PDF, save the pages with PDF to JPG.
• If you can scan the paper again, choose a lower resolution on the scanner. A smaller picture to start with gives a smaller PDF.
• A PDF with a password, or with limits set by its owner, is refused. Remove them first with Unlock PDF and the right password; the site never guesses passwords.
• A digitally signed PDF needs a tick first, because compressing it makes the signature show as invalid. Keep the signed original if you may need to prove it is genuine.

Everything happens in your browser: your file is never uploaded to any server. You can check: once your file is open, turn on airplane mode — the tool still works.

Questions

More tools