How to Compress a PDF Without Adobe Acrobat

The answer is decided by what is inside the PDF. A scan of photographs and a text-only contract fail for opposite reasons, and a tool that fixes one can inflate the other.

Missing from that table: any reason to subscribe to Acrobat. Also missing: a single winner. Keep reading only as far as the row that matches your file.

Two files, chosen because they break differently, and both reproducible.

Sizes are raw bytes. Image geometry comes from pdfimages -list, and every output was checked with pdftotext to confirm the text layer survived. It did, in every route below, with one caveat noted in the Ghostscript section.

Open the PDF, choose File → Export, and set the Quartz Filter pop-up to Reduce File Size. Apple documents exactly that in the Preview User Guide, with the warning that “when compressed, the PDF may be of lower quality than the original”.

Measured:

On photographs it is excellent and instant. On text it does essentially nothing, because there are no images to resample, and on some text-only PDFs it makes the file larger — a failure mode covered in detail in what Preview’s Reduce File Size actually does to your PDF.

The reason there is no quality slider is that the settings are baked into a file on your disk. It is a 949-byte plist, and you can read it:

plutil -p "/System/Library/Filters/Reduce File Size.qfilter"

Our 4,032 px page images came out 2,111 × 1,583 at exactly 144 PPI, which is the filter doing precisely what it says. Whether 144 is right for your document is a question Preview never asks you.

One thing worth knowing on macOS 27: the same Export sheet also offers Create Linearized PDF, Optimize images for screen and Save images as JPEG as separate checkboxes. They are cruder than the filter and they are free, so they are worth a try on a stubborn file before reaching for anything else.

Yes, and it is the best-kept free trick on macOS. Quartz filters are just plists, and Preview will use any filter it finds in ~/Library/Filters. Open ColorSync Utility (in Applications → Utilities), go to the Filters tab, duplicate Reduce File Size, and change the numbers. Your copy appears in Preview’s Quartz Filter menu immediately.

Two copies of the filter, differing only in three values, on the same photo PDF:

That last row is the one Acrobat users buy Acrobat for: a compression pass that keeps print resolution instead of flattening everything to 144 DPI. It costs nothing, it uses software Apple already gave you, and the only reason more people do not do it is that ColorSync Utility is not somewhere anyone looks.

For raw squeezing of image-heavy files, it is the strongest free option there is, and it is also the one most likely to surprise you. Install it with Homebrew:

brew install ghostscript
gs -q -dNOPAUSE -dBATCH -sDEVICE=pdfwrite \
   -dPDFSETTINGS=/ebook -sOutputFile=out.pdf in.pdf

Ghostscript 10.07.0, four presets, both files:

Three things in that table deserve explaining rather than glossing over.

/screen is astonishing and slow. 372 KB from 24.9 MB, a 98.5% cut, but it took 12.2 seconds for six pages and it resampled the images to 1,056 × 791 at 72 PPI. That is a thumbnail. It is the correct answer for an email attachment and the wrong one for anything that gets zoomed.

/printer did nothing at all. Ghostscript only downsamples an image when it exceeds the target resolution by a threshold factor. Both numbers are in Ghostscript’s own Resource/Init/gs_pdfwr.ps: /printer sets /ColorImageResolution 300, and the shipped default is /ColorImageDownsampleThreshold 1.5. So nothing is touched below 450 PPI, our images sit at 275, and the file came back 789 bytes larger than it went in. Not a bug. A documented policy that catches people out constantly.

It grew the text file by more than a third. Every preset made license.pdf bigger, /printer by 44.4%. The text itself came through: 71,485 characters extracted before, 71,643 after. What changed is structure. A 69-object file came back as a 695-object file, and the decompressed content grew from 254,069 to 300,687 bytes. Ghostscript rebuilds a PDF from scratch, and rebuilding something that was already small and tidy costs you.

Rule of thumb: Ghostscript is the right tool when the PDF is mostly pictures and you are willing to wait. Point it at a word-processor PDF and you will usually make things worse.

They work, they need nothing installed, and they are the right call on a borrowed computer. We have not benchmarked them here, because doing so honestly means uploading the test files and the whole point of the section is that you should think before you do that.

The limits are where the business model lives. iLovePDF’s free tier caps a Compress task at 2 files and 200 MB; Premium is $4/month billed annually, which is $48/year and still an ongoing bill. Smallpdf, Adobe’s own web tool and the rest run comparable meters. We have written these up in more detail as an iLovePDF alternative and a Smallpdf alternative.

The part that actually matters is not the file limit. If the PDF is a signed contract, a medical record, a passport scan or an NDA, the upload is the problem and the file size is a detail. Preview is on the machine already and it never sends anything anywhere.

Several, and they are all one-time purchases in the price range of two months of Acrobat. PDF Squeezer is $19.99. Smol is $29 and covers images, video, audio and PDFs rather than PDFs alone. Both run locally.

What a preset ladder buys you over Preview’s single button is the ability to pick a rung. Smol’s five presets are long-edge pixel caps, not DPI targets, which means the result is predictable across page geometries. Measured on both test files:

The same ladder is what makes an oversized Office export tractable, since both a PowerPoint and a Word document usually arrive here as a PDF that is still too big for whatever is rejecting it.

Two honest readings of that table. The photo column is a real ladder: pick the rung that fits the upload limit and the quality you need. The licence column is flat at −3.9% because there are no images to resample, which is the same reason Preview managed −0.4% and the reason the only tool that moved that file at all made it bigger. A text-only PDF is already close to as small as a PDF gets.

The text layer came through all five presets unchanged, at 71,485 characters, identical to the original. Both files together took 530 ms at tiny. The preset behaviour is explained properly in PDF compression presets, explained, and the field is ranked in the best PDF compressor for Mac.

Quite a lot, and pretending otherwise would be dishonest. Adobe advertises Acrobat Pro with “Turn scans into editable PDFs”, “Redact sensitive content”, “Create web forms” and “Compare PDFs to review differences”. Nothing on this page does any of them.

If you run OCR on scanned archives, if you redact documents where a failed redaction is a legal problem, if you build fillable forms, or if you live in a prepress workflow that needs PDF/X output and preflight, Acrobat is the tool and $239.88 a year is a business expense rather than a rip-off.

If what you do is make files small enough to send, you are renting a workshop to hang one picture. The side-by-side is in our Acrobat alternative for Mac comparison rather than repeated here.

For one image-heavy PDF that needs to go out in the next two minutes, use Preview. Three clicks, free, already installed, and it took 84.2% off our test file. Paying anything for that single job would be silly.

If 144 DPI is wrong for your document, build a custom Quartz filter in ColorSync Utility. It is still free, it takes five minutes once, and it gave a better result than the stock filter on every measure we tried.

If you want the absolute smallest file and can wait twelve seconds, Ghostscript’s /screen beat every other route in this article by a factor of six. It is free and open source and it will keep being free.

Where a paid app earns its keep is the folder: thirty PDFs a week, the same settings each time, a preset ladder instead of a single button, and nothing leaving the machine. That is the batch case, and it is why Smol is a one-time $29 rather than a subscription. For a single file, everything above is free and we would rather you used it.