A big PDF — a scanned contract, a slide deck, an image-heavy report — is often too large to email or upload. On a Mac you can make it smaller in a few ways, and for most people the one to try first is already installed and free. Here are the honest options, with the trade-offs stated plainly.
If you just need a PDF to be smaller and you're not fussy about the exact result, use Preview — it's built into every Mac and costs nothing. If you need control over how small (and how much quality you keep), or the document is confidential, read on.
The catch: Preview is a general-purpose document viewer, not a dedicated compression tool, so it gives you no control. It applies one fixed level of compression — you can't dial it up or down — so on some files it over-compresses (photos and scans come out soft or blurry), and on others it barely helps or even makes the file slightly larger. There's no estimate before you save; you find out afterwards whether the result is usable. And each PDF is its own round trip — open the file, choose Export, find the Quartz Filter menu, save, check the result — with no batch option. For occasional documents it's perfectly adequate. If you compress PDFs regularly, the extra steps become noticeable.
If you're happy on the command line, Ghostscript is free, runs entirely on your Mac, and lets you pick a level. Install it with Homebrew:
brew install ghostscriptThen compress a file:
gs -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook \
-dNOPAUSE -dQUIET -dBATCH \
-sOutputFile=smaller.pdf original.pdfSwap /ebook for /screen (smaller, lower quality) or
/printer (larger, higher quality).
The catch: this is a power tool, not a convenience. You're installing a command-line toolchain to shrink a document, the settings are opaque presets, and — like Preview — you see nothing until it's done, so getting the balance right is trial and error. It genuinely works, but if you don't already use the Terminal, it's unlikely to be the most convenient everyday option.
Sites like iLovePDF, Smallpdf and Adobe's online tools compress a PDF in your browser in a couple of clicks, and they work well.
The main catch: online compressors work by uploading your PDF to the provider's servers — the point at which you lose direct control of the document. Many reputable services explain how they handle and delete uploaded files, and for a restaurant menu or a holiday itinerary that's usually an inconsequential trade-off. A passport scan, a bank statement, a legal contract, a medical letter or a board paper is different. Whether that's acceptable is your call — but if you'd rather the document never left your Mac, an offline tool removes the question altogether.
The practical ones: you need a connection (no use on a plane or an unreliable train), big files upload slowly, and free tiers often cap file size or daily use.
Most people never need more than Preview. Here's the quick way to tell:
Free · built into every Mac
Free tiers
£2.99, once
Light Touch is a small Mac app (£2.99, Mac App Store) built for exactly the gap the options above leave. Preview works, but it isn't built for this one job: you open the PDF, choose Export, find the Quartz Filter menu, save a new file, and only then find out whether the result is any good. Light Touch starts from the PDF itself — drop it on, nudge one slider if you want to, and press Compress. You never open the file or go looking through menus, and it takes a batch as happily as a single PDF: drop in ten, and one slider applies to all of them. If your week involves a stack of PDFs rather than the odd one, batch handling may justify the price on its own.
And the rest is built to take the guesswork out too:
Light Touch doesn't replace Preview — it makes PDF compression easier to control. You decide how much to compress, see the estimated file size before committing, compress a whole batch together, and keep every document on your Mac. If Preview's one-tap result is good enough for you, honestly, keep using Preview. If it isn't, that's exactly why Light Touch exists — not to compress PDFs differently, but to make the whole process predictable.
Compression shrinks the images inside a PDF by lowering their resolution and quality. Tools like Preview apply a single fixed level, so a photo-heavy or scanned PDF can come out soft. The fix is control: choose a gentler level so the text stays crisp and images stay legible.
Yes. Preview, Ghostscript and Light Touch all run entirely on your Mac, so nothing is uploaded. Only online compressors send your file to a server. For confidential documents, use an offline tool.
It can. Compression discards some image detail, so the more you shrink a file, the more visible the loss. Selectable digital text is usually preserved; photos, scans and other embedded images are where visible quality drops. A tool that lets you choose the level — and shows the estimated size — lets you find the balance instead of guessing.
Use Preview: open the PDF, choose File → Export, and pick the Reduce File Size Quartz filter. It's free and built in. For more control at no cost, use Ghostscript on the command line.