How to compress a PDF on a Mac or iPhone
Checked against our tools on 18 October 2026
On a Mac, open the PDF in Preview, choose File > Export, set Quartz Filter to Reduce File Size and save under a new name. It's built in and free, but it applies one harsh setting to every image, so scans and photos often come out blurry, and a mostly-text PDF can even get bigger. When that happens, open Compress PDF in Safari or Chrome and pick Medium: in our tests a 3-page scan went from 2.42 MB to 533 KB. On an iPhone, there's no compress button in the Files app; use Compress PDF in Safari, or the Optimize File Size of PDF action in Shortcuts.
Go straight to the tool: Compress PDF, Remove pages, Split PDF
Compress a PDF with Preview
Preview comes with every Mac, so this works the same on a MacBook Air, MacBook Pro, iMac or Mac mini.
- Open the PDF in Preview. Double-clicking usually does it; if another app opens instead, Control-click the file and choose Open With > Preview.
- Choose File > Export. Not Export as PDF: that window has no filter menu.
- Leave Format on PDF and set Quartz Filter to Reduce File Size.
- Give the file a new name, so you keep the original, and select Save.
- Open the new file and zoom to 100% on a page with a photo or a signature before you send it.
Why Preview's result is often blurry
Reduce File Size has no quality setting. It shrinks and re-encodes every image in the file the same way, whether it's a photo, a scanned contract or a chart, so a scan that was perfectly readable can come out soft enough that small print and signatures smear. You can't ask it to go easier.
It also rewrites the whole file, and on a PDF that's mostly text that can add more than it saves. If the exported file is larger than the original, keep the original: there were no big images to shrink.
ColorSync Utility, also built into macOS, can make a gentler custom filter, but it takes some trial and error. Most people are better off with a tool that has levels.
When Preview isn't good enough
Compress PDF works in Safari, Chrome or Firefox on a Mac with nothing to install. It has three levels. Light only tidies the file's structure and never touches an image. Medium re-encodes photos and scans at up to 2,200 pixels on the long side, which keeps text and signatures readable. Strong goes down to 1,500 pixels and also converts screenshots. Text, fonts and vector drawings are never re-encoded at any level.
| Sample | Original | Medium | Strong |
|---|---|---|---|
| 3-page office scan (300 DPI) | 2.42 MB | 533 KB | 266 KB |
| 4 pages of large photos | 12.49 MB | 3.22 MB | 272 KB |
| 1-page report with a PNG screenshot | 2.28 MB | Not reduced | 90 KB |
What happens to your file
Preview never sends your file anywhere. Compress PDF does upload it, because it needs server software: the upload is encrypted, processed in an isolated worker and deleted automatically about 60 minutes later, or straight away from the result screen. If you'd rather keep the file on your Mac, Remove pages and Split PDF also make a PDF smaller and run entirely in your browser.
Compress a PDF on an iPhone or iPad
The Files app can preview, mark up and rotate a PDF, but it can't make one smaller. Two ways that work:
- In Safari, open Compress PDF, tap the box and choose the file from Files, pick a level and download. The smaller copy lands in the Downloads folder in Files.
- In the Shortcuts app, make a shortcut with the Optimize File Size of PDF action, turn on Show in Share Sheet, then share a PDF to it. It's quick and stays on your phone, but like Preview it gives you no say in the quality.
Common questions
Is it free? Preview and Shortcuts are part of macOS and iOS. Compress PDF is free too: without an account it takes files up to 25 MB and 2 compressions a day, and a free account raises that to 50 MB and 10 a day.
Can I get a PDF under 1 MB on a Mac? A few scanned pages at Strong usually get there. For a long photo report, remove pages or split it as well; our guide to reducing PDF file size covers that, along with Gmail's and Outlook's attachment limits.
Will compressing break a signature? A drawn signature stays, though it can blur in Preview. A certificate-based digital signature stops being valid after any compression, because the file is rewritten. Compress first, then sign.