How to Compress PDF in Mac

Preview on macOS ships with a Reduce File Size filter that halves most PDFs in three seconds, and most Mac users never notice it exists. This guide covers that filter, the two ways to fix its known quality problem, the Automator workflow that saves the tweaked filter forever, and the browser fallback for the times when Preview goes too aggressive. It applies to macOS Sonoma, Ventura, and every version back to Big Sur. It works on Intel Macs and Apple Silicon. And it covers scanned documents, image-heavy PDFs, and Word-exported files. The starting file gets cut by 50 to 90 percent in about a minute of active work. Read on for the step by step, the tuning tricks that keep quality, and eleven direct answers to the questions Mac users ask most about compressing PDFs.

Why Preview's built-in filter isn't enough by itself

Preview's Reduce File Size filter uses a fixed Quartz filter that ships with the OS. The filter drops images to 72 DPI. That works for text heavy PDFs but destroys scans and photo pages. A 4 MB scanned certificate goes from 4 MB to 400 KB, but the small print at the bottom of the page turns unreadable.

The fix is a custom Quartz filter that sets image resolution to 150 DPI instead of 72 DPI. That change costs 20 percent extra file size and delivers roughly triple the visual clarity. Once you save the custom filter, it appears alongside the default one in Preview forever.

Method 1: the built-in Reduce File Size filter (30 seconds)

Built-in method takes 30 seconds and works for any PDF where extreme compression is fine. Open the PDF in Preview. From the menu bar, choose File and Export. In the Quartz Filter dropdown, select Reduce File Size. Give the file a new name (so you don't overwrite the original), pick a destination, and click Save. Preview creates the compressed copy immediately.

Expect a size drop of 50 to 90 percent depending on the source. A scanned certificate at 4 MB usually comes out around 400 KB.

Method 2: custom Quartz filter for better quality

Custom filter method takes about five minutes to set up once and stays available forever after. Open ColorSync Utility (search for it with Spotlight). Click the Filters tab. Duplicate the "Reduce File Size" filter by clicking the down arrow at its right edge and choosing Duplicate Filter. Rename the copy to something like "Reduce File Size 150 DPI". Expand Image Sampling in the new filter. Change Resolution to 150 pixels per inch and Quality to Medium. Save.

Back in Preview, when you export the PDF and open the Quartz Filter dropdown, your new filter appears in the list. Pick it. Save. The file comes out at maybe 700 KB instead of 400 KB, but text and images look sharp.

Method 3: browser-based compression for exact target sizes

When you need a specific target like 100 KB or 500 KB, Preview's filter can't do it because you can't specify a size. Switch to a browser tool. The PDF Compress homepage lets you pick a target and downloads the compressed file in a few seconds. Landing pages for common sizes like compress PDF to 500 KB preset the target so you skip the size picker.

This approach works from Safari, Chrome, and Firefox on Mac. It also works from Safari on iPad and iPhone, so you can compress the same file from another Apple device if the Mac is elsewhere.

Method 4: Ghostscript on Terminal (advanced)

Terminal method needs Homebrew and about ten minutes of setup, but gives you granular control forever after. Install Homebrew from brew.sh. Then run brew install ghostscript. To compress a PDF, run:

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.5 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

Change /ebook to /screen for aggressive compression, or /printer for high quality. The output file lands in the current directory. This is the same engine PDF Compress runs on the server. Running it locally means the file never leaves the Mac.

Comparing the four methods on a real file

A test on a 4.2 MB scanned certificate produced these results:

• Preview default filter: 380 KB output. Small print blurry.
• Preview custom filter at 150 DPI: 720 KB output. Small print sharp, images clean.
• Browser tool with 500 KB target: 495 KB output. Balanced quality, hits target.
• Ghostscript /ebook preset: 610 KB output. Quality similar to custom Preview filter.

The right method depends on your priority. For a single strict target size the browser tool wins. For unlimited runs at good quality the custom Preview filter wins. For automation Ghostscript wins.

Preserving text search after compression on Mac

Compression doesn't remove selectable text from a PDF. Preview's filter keeps the text layer intact, and so do the browser tool and Ghostscript. What compression can't do is add text to a PDF that lacks it. If your file is a scan without an OCR pass, Command F won't find anything after compression because there was nothing to find before.

To add OCR on Mac, open the PDF in the free version of Adobe Acrobat Reader, or use Apple's built-in Live Text (open the PDF in Preview, click into an image, and text becomes selectable). Save the OCR'd copy, then compress that copy.

Common problems and fixes on macOS

Three problems come up often when compressing PDFs on Mac, and each has a straightforward fix.

• Preview says the file can't be exported: the PDF has DRM protection or a password. Remove the password first through File and Export as PDF, or unlock it through the source app.
• Custom Quartz filter doesn't appear in Preview: restart Preview after saving the filter in ColorSync Utility. Some macOS versions cache the filter list.
• Ghostscript command not found: the Homebrew binaries aren't on the PATH. Run eval "$(brew shellenv)" or restart Terminal.

If you're compressing to a specific number like 100 KB, jump to the sibling walkthrough on how to compress PDF file to 100 KB which covers the target size approach in more depth.

Frequently asked questions

Can Preview compress a PDF without downloading extra software?

Yes. Preview ships on every Mac. File and Export with the Reduce File Size Quartz filter cuts most PDFs by 50 to 90 percent without any download.

What is a Quartz filter?

A Quartz filter is a macOS-specific set of image processing rules applied when Preview or ColorSync Utility exports a document. The Reduce File Size filter downsamples images to 72 DPI and re-encodes them as JPEG.

Which is better on Mac: Preview or an online tool?

Preview wins for privacy because the file never leaves your Mac. Online tools win for exact target sizes and for machines without Preview (Windows, Linux). Pick based on what matters more for that job.

Does Preview keep text selectable after compressing?

Yes. The text layer inside the PDF is preserved. Only images are re-encoded. Command F still works after compression.

Which macOS versions support the Reduce File Size filter?

Every macOS version since Snow Leopard (2009). The filter is part of the Quartz imaging system. If your Mac runs macOS, it has this filter.

Is there a size limit for Preview compression?

Preview handles files up to a few hundred megabytes. Above that, the export dialog can hang. For very large PDFs, split them into chapters in Preview first, then compress each chapter.

Can I compress multiple PDFs at once on Mac?

Yes, through Automator. Create a Quick Action that runs the Apply Quartz Filter to PDF Documents step, save it, then right-click a folder of PDFs in Finder and pick your action. Every PDF gets compressed in place.

Which is faster: browser compression or Preview?

Preview finishes in about three seconds for a typical PDF. Browser tools take five to ten seconds because of upload time. Preview wins on speed, browser wins on target size precision.

Does compression change how the PDF prints?

No. Print output uses the highest resolution version of images inside the PDF, which for a compressed file is the compressed version. The visible quality on paper matches the on-screen preview.

Can I revert a compressed PDF back to the original?

No. Compression is one-way. Keep the original file. Preview creates a compressed copy at export time; the original stays untouched only if you exported to a new filename.

Which method preserves colour accuracy best?

The custom Quartz filter at 150 DPI Medium quality keeps colour accuracy close to the original. The default Reduce File Size filter shifts colour slightly because it converts colour profiles during compression.

Where can I contact the team behind these guides?

The contact page lists the form and response time. Every guide is reviewed against the site's editorial standards before publishing.

Automator workflow for batch PDF compression on Mac

Automator turns a one-off Preview compression into a folder action that runs on any PDF you drop into it. Setup takes ten minutes and pays back within the first week if you compress more than five PDFs a month.

Open Automator. Choose Quick Action for the document type. Set "Workflow receives" to PDF files. Add the action "Apply Quartz Filter to PDF Documents". Pick the custom filter you created earlier (or Reduce File Size for the default). Add "Move Finder Items" and point it to a Compressed folder in your Documents. Save the workflow with a name like "Compress PDF to 150 DPI".

Now right-click any PDF in Finder, choose Quick Actions, and pick your workflow. The compressed copy appears in the Compressed folder. Select multiple PDFs and run the action once to batch them all in a single pass.

Preview limitations to know about

Preview handles most PDFs but stumbles on three categories.

• Password-protected PDFs: Preview can display them if you know the password but can't apply the compression filter until you save an unlocked copy first.
• PDFs with form fields: compression through Preview usually preserves fields but occasionally flattens them into images. Test on a copy before applying to the original.
• PDF/A archival files: Preview's compression breaks PDF/A compliance. Files needed for legal archives should stay uncompressed or use a PDF/A aware tool.

For jobs Preview can't handle cleanly, jump to the browser tool with a target size. That handles password-free PDFs of most types.

Does Preview compress PDFs saved from Pages or Numbers?

Yes. Any PDF Preview can open, it can compress. Pages and Numbers exports handle the compression well because they use standard PDF fonts and images.

Which macOS version has the best Preview compression?

macOS Sonoma and later ship with the most stable Quartz filter engine. Older versions work but occasionally produce PDFs with corrupted colour profiles on complex source files.

Can I chain Preview compression with another tool?

Yes. Run Preview's Reduce File Size first, then process the output through Ghostscript or a browser tool if the size is still too big. Multi-pass compression stacks JPEG artefacts, though, so use it only when a single pass can't hit the target.

Which Mac app produces the smallest PDF output?

Ghostscript with the /screen preset produces the smallest files, but at the cost of visible image quality. For balanced output, the browser tool with a specific target size beats every Mac-native option because it iterates through settings automatically.

Can Preview export part of a PDF instead of the whole file?

Yes. Open the PDF, show the thumbnail sidebar (Command Option 2), select the pages you want, then drag them to the desktop or use File then Print. The result is a smaller PDF containing only those pages, and it compresses further from that reduced starting point.

Does the Preview compression work offline?

Yes. Preview's Reduce File Size runs entirely on the Mac. No internet needed. That's the main reason to keep it in the toolkit even after installing Ghostscript.

Try the custom Quartz filter first. If it still doesn't hit the size limit your portal demands, drop back to the browser tool with a specific target and check that the output looks acceptable at that size.