Mac users have a few options for reducing PDF size that Windows users don't — built-in tools that handle basic compression without installing anything. But these built-in options have real limitations, and knowing when they're adequate and when you need something more powerful saves a lot of trial and error. Here's the full picture.
Preview: The Built-In Option and Its Limits
Preview, the default PDF viewer on Mac, has a built-in compression option that most people don't know about. To use it: open the PDF in Preview, go to File > Export as PDF, then click the Quartz Filter dropdown and select "Reduce File Size."
This works — but with a significant catch. The Reduce File Size filter in Preview applies aggressive compression with no quality control. On image-heavy documents it often produces results that are visibly degraded: blurry photos, pixelated charts, and text that looks slightly soft. There's no slider, no quality setting, no preview of the output before you commit.
Preview's compression is acceptable for documents where visual quality is not a concern — internal drafts, text-heavy reports with minimal images, anything being used for reference rather than presentation. For anything client-facing, visual, or print-bound, the quality loss is usually too much.
Print to PDF: A Lighter Touch
A gentler alternative to Preview's compression filter: open the PDF, go to File > Print, then click the PDF dropdown in the bottom-left of the print dialog and choose "Save as PDF." This creates a new PDF by re-rendering the document through macOS's PDF engine.
The result is a cleaner, stripped-down file — metadata removed, some redundant data eliminated — but without the aggressive image compression of the Reduce File Size filter. File size reduction is more modest (typically 10-30% rather than 50-80%), but quality is preserved. This is the better built-in option for documents where appearance matters.
ColorSync Utility: The Hidden Mac Tool
Most Mac users have never opened ColorSync Utility, but it has a PDF filter editor that lets you create custom compression settings — unlike Preview's single fixed filter. Open ColorSync Utility (find it in Applications > Utilities), go to the Filter tab, and you can create a custom Quartz filter that compresses images to a specific quality level rather than blindly applying maximum compression.
This takes some setup: create a new filter, add an image compression component, set quality to something like 0.6-0.75 (rather than the 0.0 that Preview's default filter uses), save it, and it appears as an option in Preview's Quartz Filter menu. The result is controlled PDF Compression that balances size reduction and quality — significantly better than the default Reduce File Size filter.
When the Built-In Tools Aren't Enough
Mac's built-in options have a ceiling. They work for straightforward cases but fall short when:
- You need to choose between specific compression levels (low, medium, high) and see the tradeoff before committing
- The file is very large and needs significant reduction without visible quality loss
- You need to compress multiple files consistently, with the same settings applied each time
- You're on someone else's Mac and don't want to set up a custom ColorSync filter
For these cases, a browser-based tool is the practical answer — no installation required, works the same on any Mac, and gives you actual control over the compression level. WukongPDF's PDF Compression tool at www.wukongpdf.com runs in any browser: open Safari or Chrome, upload the file, choose low, medium, or high compression, and download the result. The compression engine is more sophisticated than Preview's filter and the quality tradeoffs are explicit rather than hidden.
Which Method to Use When
- Internal draft, quality doesn't matter: Preview's Reduce File Size filter — fast, no setup
- Need quality preserved, modest size reduction: Print to PDF
- Regular use, want controlled compression: custom ColorSync filter in Preview
- Client-facing document, need best quality-to-size ratio: browser-based tool like WukongPDF