How to compress a PDF (and get it under an email limit)

Why is my PDF so big?

Almost always, it’s the pictures. Text is cheap to store — a PDF of a long, text-only report is usually small, because each letter is just a character code and a reference to a font. Images are the heavy part, and some PDFs are made of nothing else.

• Scanned documents. A scanner or scanning app saves every page as a photo of the page. Ten pages means ten full-page images.
• Photos from a phone. Modern phone cameras take very large images. Drop a few into a Word document or a PDF and they’re often kept at full size, even though they’ll only ever be seen a few inches wide on a screen.
• Design-heavy files. Brochures, menus and slide decks exported to PDF often carry high-resolution artwork meant for professional printing.

That’s why compressing a PDF really means compressing the images inside it. Knowing what’s in your file tells you how much you can expect to save:

How to compress a PDF in your browser

This works on Windows, Mac, Chromebook, iPhone and Android, with nothing to install.

1. Open Compress PDF and drop your file in (one PDF at a time, up to 60 MB).
2. Choose a level. Less compression keeps images closest to the original with a modest saving. Recommended lowers image quality slightly for a solid saving with almost no visible difference. Smaller file also reduces very high image resolutions to a more typical screen size — the biggest saving, but it can show if you zoom right in.
3. Check the result. You’re shown exactly how much smaller the file got before you download anything.
4. Save the smaller PDF. Your original isn’t changed.

Only the embedded photos and scans are touched. Text, fonts and vector graphics stay exactly as they were, so the document is still sharp, selectable and searchable — it is never flattened into one big picture per page, which is how some compressors cheat their way to a smaller number.

And because the whole job happens inside your browser tab, the PDF never leaves your device. That matters for the files people most often need to shrink: payslips, bank statements, signed contracts and ID scans heading to a landlord, an employer or a mortgage broker.

How to reduce PDF size on a Mac with Preview

Preview has a built-in option:

1. Open the PDF in Preview.
2. Choose File → Export.
3. In the Quartz Filter menu, choose Reduce File Size.
4. Give the file a new name so you keep the original, then click Save.

It’s free and private, but it’s a blunt instrument: Apple itself notes the result may be lower quality than the original, and on scans it can leave text looking soft or blotchy. Open the new file and zoom in before you send it. If it’s too rough, use a tool with a gentler setting instead.

If you made the PDF yourself, go back to the source

Compressing a finished PDF is a repair job. If you still have the original Word document, it’s often better to make a smaller PDF in the first place:

• In Word for Windows, use File → Save As, choose PDF as the file type, and pick Minimum size (publishing online) instead of Standard. That setting mainly lowers image quality, which is exactly where the size is.
• Before exporting, you can also select a picture and use Picture Format → Compress Pictures to shrink the images in the document itself.
• When scanning, choose greyscale or black and white for plain text documents, and a moderate resolution. Colour scans at the highest setting are the single biggest cause of huge PDFs.

If you’re starting from a Word file anyway, our guide on converting Word to PDF covers the export options in more detail.

What about Windows, iPhone and Android?

Windows doesn’t include a PDF compressor, and neither iPhone nor Android has an obvious built-in one in its Files app. The usual answer is either a paid PDF editor such as Adobe Acrobat, an online service (most of which upload your file to their servers to do the work), or a browser-based tool that runs on the device itself. Compress PDF is the last kind, so it works the same way in Safari on an iPhone as in Chrome on a laptop.

Still too big to email? What to try next

Email services cap attachment sizes — Gmail’s limit for personal accounts is 25 MB, and many other providers and workplaces set theirs lower. Attachments also grow a little when they’re encoded for sending, so aim comfortably under the limit rather than just below it. If compressing hasn’t got you there:

1. Cut what isn’t needed. Blank scans, duplicate pages and cover sheets all add weight. Delete PDF Pages removes them.
2. Send it in parts. Split the PDF into two or three files and send them in separate emails. Our guide on how to split a PDF walks through it.
3. Rescan it. If it’s a scan, scanning again in greyscale at a lower resolution usually beats any amount of compression afterwards.
4. Send a link instead. Put the file in cloud storage and share a link. Gmail does this for you automatically, swapping an oversized attachment for a Google Drive link.

Does compressing a PDF reduce quality?

It reduces the quality of the images inside it — that’s where the saving comes from. At a sensible level the difference is hard to see on screen, which is all most emailed documents ever need. Where it can matter is fine detail you’ll zoom into or print large: small print on a scanned receipt, a detailed diagram, a photo for a printed brochure. For those, use the lightest level that gets you under your limit, and always keep the original.

Common questions