How to reduce PDF file size

Work out what's making it big

A PDF's size comes almost entirely from images: scanned pages, photos, screenshots. Text is tiny, because the file stores characters and a font rather than a picture of each letter. A 12-page text document we tested was 26 KB; one scanned page at 300 DPI was about 800 KB.

So the useful question is how many images the file has and how large they are. If it's a scan or a photo report, compression will help a lot. If it's a long text document that's still large, it probably embeds big fonts or has hundreds of pages, and removing or splitting pages will do more than compressing.

1. Compress it

Compress PDF re-encodes images at a lower quality or resolution and tidies the file's structure. It has three levels:

• Light only tidies structure and never touches an image, so nothing gets blurrier. On image-heavy files it often changes little.
• Medium re-encodes photos and scans. This is the one to try first.
• Strong lowers resolution further and also converts screenshots and other lossless images, which Medium leaves alone. Check the result at the zoom you'll actually read it at.

What compression did in our tests

How compression handles your file

Compression uploads your file, because it needs server software; Remove pages and Split PDF don't. The upload is encrypted, processed in an isolated worker and deleted automatically about 60 minutes later, or sooner if you delete it from the result screen. If the result isn't smaller than the original, we say so and you keep the original. Our guide on why a compressed PDF is still too large explains the cases where it can't help.

2. Remove pages nobody needs

Cover sheets, blank scanned backs, appendices the recipient already has: each page you drop takes its images with it. Remove pages runs in your browser, so the file stays on your device, and when it saves the new PDF it drops anything only the removed pages used. On a scan, removing half the pages roughly halves the file.

3. Split it into parts

When every page matters and the file is still too big, send it in pieces. Split PDF cuts it by page ranges, such as 1-20 and 21-40, and gives you a ZIP of the parts. Name them so the order is obvious, like report-part-1-of-2.pdf. Splitting also runs in your browser.

Email attachment limits

Gmail and Yahoo Mail accept attachments up to 25 MB, and Outlook.com up to 20 MB. Gmail turns anything bigger into a Google Drive link, and Outlook offers OneDrive instead. Company mail servers often set lower limits, sometimes 10 MB.

Attachments also grow by about a third on the way, because email encodes binary files as text, and some servers count that larger size. If a 19 MB PDF bounces from a 20 MB limit, that's why. Aim for 15 MB or less and it will get through almost anywhere.

What won't help

Zipping a PDF barely changes its size, because the images and text inside are already compressed. Saving it again with Print to PDF can make it bigger, since some printers turn every page into an image. And converting a scan to Word or back won't shrink anything; the pictures come along.

If you made the scan yourself, the best fix is at the scanner: 200 DPI in greyscale is plenty for a signed form or a letter, and gives a far smaller file than compressing a 600 DPI colour scan afterwards.

Common questions

Is it free? Yes. Without an account, files can be up to 25 MB. A free account raises that to 50 MB and allows 10 compressions a day.

Will compression make the text blurry? No. Text, fonts and vector drawings are never touched; only images are re-encoded.

Can I get under 1 MB? Usually, for a few scanned pages at Strong. For dozens of photo pages, split the file too.