How to Compress a PDF on a Mac for Free (Preview, Quartz Filters, and When to Use a Target-Size Tool)

Updated November 2, 2026 · 4 min read · By LeDeuxions

The situation

You exported a PDF on your Mac and it turned out far bigger than expected. Maybe it is a scanned contract, a slide deck full of photos, or a portfolio you need to email. Now a form rejects it, or your mail client warns the attachment is too large.

The good news is that macOS already includes tools that can shrink a PDF without any paid software. The tricky part is that the built-in option is blunt: it gives you one result and no way to aim for a specific size. Knowing which route fits your file saves a lot of trial and error.

Why Mac PDFs get big

Most oversized PDFs are heavy for one reason: images. A PDF is a container, and if it holds full-resolution photos or high-DPI scans, the file inherits all those pixels. A single page scanned in color at a high resolution can be several megabytes on its own.

Text-only PDFs are usually small because text is stored as compact instructions, not pixels. So when a file is surprisingly large, it is almost always image data, embedded fonts, or leftover high-resolution graphics driving the size up, not the words on the page.

Method 1: Preview's Reduce File Size

Preview is the fastest free route and needs nothing extra.

Open the PDF in Preview (it is the default PDF viewer on macOS).
From the menu bar, choose File, then Export.
In the export dialog, open the Quartz Filter menu and select Reduce File Size.
Give the file a new name so you keep the original, then save.

This works well for photo-heavy PDFs. The weakness is that it is a fixed setting: sometimes it barely shrinks the file, and sometimes it over-compresses and makes text or images look soft. If the single result it gives you is wrong, you cannot nudge it from this dialog alone.

Method 2: A custom Quartz filter for more control

If the default filter compresses too aggressively or not enough, you can build your own.

Open ColorSync Utility (search for it with Spotlight).
Go to the Filters tab and duplicate the existing Reduce File Size filter.
Expand your copy and adjust the image settings, such as the resolution cap and the JPEG quality, to a gentler or stronger level.
Save it, then reopen your PDF in Preview and pick your new filter under File, then Export.

This gives you finer control than the one-size setting, but it is still manual. You are guessing at values, exporting, checking the size, and repeating. For an occasional file that is fine; for a hard size limit it gets tedious.

When to use a target-size tool instead

Preview and Quartz filters answer "make it smaller." They do not answer "make it fit under 10 MB." When a portal, court, or email rule gives you an exact ceiling, guessing wastes time.

A target-size tool flips the logic: you state the size you need and it works backward to hit it. PDF300 lets you enter a target file size and compresses the PDF to fit. It also offers an in-browser mode where the file is re-encoded locally and never leaves your Mac, which matters for anything private. For a stubborn file, that is faster than exporting from Preview over and over. You can try it at PDF300.

Checklist

Confirm the real culprit is images: a text-only PDF rarely needs compression.
Try Preview's Reduce File Size first; it is free and takes seconds.
Always export to a new filename so you keep the original intact.
Open the result and check that small text and photos are still legible.
If you have an exact size limit, use a target-size tool rather than guessing with filters.
For sensitive documents, prefer a route that processes the file on your own device.

FAQ

Does Preview reduce PDF quality when it compresses?

Yes, Reduce File Size lowers image resolution and quality to save space, so photos and scans can look softer. Text usually stays sharp because it is not stored as pixels. Always compare the output to the original before you send it.

Why did Preview barely shrink my PDF?

The built-in filter uses one fixed setting, so a file that is already near that resolution sees little change. It can also do little for PDFs that are large because of fonts or vector graphics rather than photos. A custom Quartz filter or a target-size tool gives you more leverage.

Can I compress a PDF on a Mac without uploading it anywhere?

Yes. Preview and Quartz filters run entirely on your Mac. If you prefer a target-size tool, PDF300 offers an in-browser mode that re-encodes the file locally, so it never leaves your device.

Written by LeDeuxions, an architect who built PDF300 after a 300 MB portal limit kept rejecting drawing sets. Figures quoted from third parties link to their source; sizes and reductions described as "typical" are estimates, not guarantees.