Compressing a PDF without Acrobat

Acrobat Pro is the default answer to "how do I compress a PDF", and it is a capable tool. But it costs a subscription, and for this specific job it has a structural limitation that no amount of money removes: there is no field for a target file size.

Worth understanding what it actually does before deciding whether you need it.

What Acrobat's compression actually is

Two features, commonly confused:

Reduce File Size applies a preset. You choose a compatibility level and it downsamples images to a fixed DPI, re-encodes them at a fixed quality, subsets fonts and discards some structure. Whatever size comes out is the size you get.

Optimize PDF (the advanced panel) exposes the individual settings — image downsampling DPI, JPEG quality per image type, font subsetting, whether to discard metadata, bookmarks, forms, JavaScript. This is genuinely powerful and the best thing about Acrobat for this task. It is also entirely manual: you set a DPI, run it, look at the file size, and adjust.

Neither lets you say "make this 200KB". You iterate by hand until it happens.

What you can do without it, for free

The two-second check first

Try to select text in the document. Whether it has a real text layer decides everything else, because a text-based PDF can usually be shrunk losslessly and a scan cannot.

macOS: Preview's Quartz filter

Preview has an export filter called "Reduce File Size". It works, and it is aggressive — often too aggressive, because it downsamples images hard with no setting to adjust. For a text document it is fine; for anything with photographs you may find it has flattened them to mush.

You can edit the filter's parameters in ColorSync Utility if you want a gentler version, which is more work than most people want.

Windows: print to PDF

Printing a PDF to the "Microsoft Print to PDF" driver re-renders it and often produces a smaller file. It also rasterises everything — the output is images of pages, so text stops being selectable and search stops working. That is a significant loss presented as a convenience, and it is the single most common way people accidentally destroy a document's text layer.

Ghostscript, if you are comfortable in a terminal

The serious free option. gs with -dPDFSETTINGS=/ebook or /screen gives you real control, handles fonts and images properly, and is what a lot of server-side compressors are running underneath.

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 \
   -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH \
   -sOutputFile=out.pdf in.pdf

Same limitation as Acrobat, though: /screen, /ebook and /printer are presets. There is no target size, so you run it, check, and change the preset.

A browser-based tool

Which brings us to the thing all of the above share.

The actual limitation of every preset-based tool

A preset is a guess made before anyone looked at your document.

/ebook downsamples images to 150dpi. On a text document with two small logos that changes almost nothing and the file stays at 4MB. On a 600dpi scan it takes 60MB to 3MB. Same preset, results differing by a factor of twenty — because the preset describes an operation, not an outcome.

So if you have been given a number — and the reason people compress PDFs is almost always that something demanded a number — a preset cannot aim at it. You run it, measure, pick a different preset, run again. That loop is the actual work, and it is the part a tool should be doing for you.

What aiming at a target looks like

Rather than applying a setting, measure the result and adjust:

Lossless rewrite only         3.1MB   over 1MB
scale 2.0 (144dpi) q0.78      4.4MB   over
scale 1.3 (94dpi)  q0.78      1.4MB   over
scale 1.05 (76dpi) q0.78      960KB   under, best so far
scale 1.15 (83dpi) q0.78      1.1MB   over
scale 1.10 (79dpi) q0.78      1.0MB   under, and the best found

Six render passes, and the answer is the highest resolution that genuinely measured under 1MB. Not a preset that happened to be conservative, and not one that happened to overshoot.

The other thing worth insisting on: the lossless pass should be tried and measured first. A structural rewrite — compressing object streams, dropping revision history, removing orphaned objects — frequently saves 30–70% on a text document, and it keeps text selectable, searchable and accessible to screen readers. Rasterising a document that could have been compressed losslessly takes something irreplaceable in exchange for nothing.

The comparison, honestly

Acrobat is better than this tool at a great many things: editing text in place, OCR, redaction, forms, pre-flight for print, accessibility tagging. If your next task is any of those, use Acrobat.

For the specific job of getting a document under a byte limit, the things that matter are whether it tries lossless first, whether it measures the real output, and whether you can name the number. Those are free to do, which is why they do not require a subscription.

Compress a PDF to 500KB, to 1MB or to 2MB does all three, in your browser, with no account and no upload. The fuller comparisons against the tools people actually use are here.

FAQ

How do I compress a PDF for free?

On macOS, Preview's "Reduce File Size" export filter works but is aggressive with images. On Windows, printing to PDF shrinks files but rasterises everything, ending text selection — avoid it if the text matters. Ghostscript gives real control from the command line. A browser-based tool that runs locally avoids both the subscription and the upload.

What does Acrobat's "Reduce File Size" actually do?

It applies a preset: images are downsampled to a fixed DPI and re-encoded at a fixed quality, fonts are subsetted, and some structure is discarded. The Optimize PDF panel exposes those settings individually, which is genuinely useful. What neither offers is a target file size field, so hitting a specific number means running it, checking, and adjusting by hand.

Does printing a PDF to PDF make it smaller?

Often yes, and at a cost most people do not realise they are paying: the print driver renders each page to a bitmap, so the output is images of pages. Text stops being selectable, search finds nothing, and screen readers get silence. For a document that only needs to be looked at, it works. For anything you might need to search or copy from, it is destructive.

Is Ghostscript better than an online compressor?

For control, yes — it handles fonts and image downsampling properly and is what many server-side compressors run internally. For hitting a specific byte target, it has the same gap as Acrobat: its settings are presets rather than outcomes, so you iterate manually. It also requires installing it and using a terminal, which is a reasonable price if you compress PDFs often and not if you do it twice a year.