Your Mac already ships with a PDF compressor, Preview: open the file, choose File > Export, set Quartz Filter to Reduce File Size, and save. It handles one file at a time. For batches, or for more control, a local app like Picmal does it from Finder without uploading anything.
That covers most one-off jobs. It falls short when you have a folder of them, when the result looks like it went through a fax machine, or when the PDF is a contract you’d rather not hand to a stranger’s server.
By Alberto Gallego. I make Picmal, so keep that in mind. The Preview steps below are free, and I’ll say plainly where they run out.
Why PDFs get big in the first place
A PDF is a container. The text inside is tiny. The weight comes from images at full resolution, embedded fonts, and any media someone dropped in.
Scans are the worst case. A scanned contract is a stack of photos of paper wearing a PDF’s clothes, and every page carries a whole photo.
So compressing a PDF mostly means shrinking those images. Where you do it matters too. Do it online and a copy of your file leaves your Mac. Do it locally and it doesn’t.
How to compress a PDF with Preview (the built-in option)
- Double-click the PDF so it opens in Preview
- Choose File → Export (not “Export as PDF”, that one has no filter menu)
- Open the Quartz Filter menu and pick Reduce File Size
- Give it a new name so you don’t overwrite the original, then save
- Select the new file in Finder and press Cmd+I to compare sizes
That’s the whole method. It costs nothing and nothing gets uploaded.
The trade-off: it works for one file, you can’t batch it, and you can’t tweak the compression. It’s a blunt filter. On image-heavy PDFs the pictures can come out soft, and now and then the result barely shrinks.
The limits of online PDF compressors
Search for a PDF compressor and the first results are web pages. Adobe’s online compressor is polished and clear about what it does, I’ll give it that. It’s still a web page.
Where they get in the way:
- Upload wait. A big PDF has to travel before it can shrink, then travel back.
- Size limits. Free tiers often cap the file or the number of files per day.
- Privacy unease. Invoices, contracts, medical letters. Your PDF takes a trip to a server you know nothing about.
- Account prompts and watermarks. Often the price of the “free” part.
A free image compressor follows the same pattern: great for the odd file, tight once it becomes a habit. For a one-off, a web tool is fine. For anything sensitive or repeated, I’d rather keep it at home.
A local PDF compressor for Mac: Picmal
This is the gap I built Picmal for. It’s a native macOS app that converts and compresses images, video, audio and PDFs on your Mac. One person makes it (me, in Córdoba, Spain).
Keep everything on your Mac
No upload. No account. The PDF never leaves your machine, so there’s nothing to trust a server with. That’s the main reason I’d pick a local tool over a web one, before speed or anything else.
Batch compress hundreds of PDFs
Preview and web tools work one file at a time. If you need to batch compress PDF files on a Mac, say a whole folder of scanned receipts, Picmal takes hundreds at once. Drop them in, run it, walk away.
If you’ve ever had to batch convert images, it’s the same idea: select everything, run once.
Fit into your workflow
It also sits in Finder as a Quick Action. Select PDFs in Finder, right-click, and run it without opening the app. If the menu isn’t showing, here’s how to enable the right-click menu.
It also works from Shortcuts and Raycast, and it can watch a folder. Point it at your Downloads or a scans folder and new PDFs get handled as they land.
Control and presets
Set the compression level once, save it as a preset, and reuse it. “Email size” for attachments, something gentler for the files you archive. The same app also splits, merges and reorders PDF pages, and turns a folder of images into a single PDF.
How it’s sold
It’s a one-time purchase, not a subscription, and updates are included. You can try the full app for 7 days, and there’s a 14-day refund. Students get 40% off with a school email.
MacStories reviewed it in November 2025 (John Voorhees, “Picmal Streamlines Batch Conversion and Compression on the Mac”). It’s had 88 releases in its first 15 months, because I keep fixing things people send me.
If you only compress a PDF twice a year, use Preview. It’s free and it’s already there.
Common mistakes when compressing PDFs
- Over-compressing. Push too hard and small print turns to mush. Start gentle, and only go harder if the file is still too big.
- Treating scans and text PDFs the same. A text-based PDF is already small, so there’s not much to win. A scan is all images, so that’s where the savings (and the damage) happen.
- Skipping the check. Open the result before you send it. Scroll through, zoom in on the smallest text, and make sure the signature is still legible.
- Overwriting the original. Always save under a new name. Once the original is gone, there’s no way back.
Where to go next
If the Preview method is enough, you’re done. If you have a pile of PDFs, or ones you’d rather keep off the internet, Picmal’s PDF compressor is the page with the details, and four free ways to compress a PDF on Mac covers the other methods. Try the full app for 7 days on your own files and see.
