Mac users have three distinct ways to reduce PDF file size — one built directly into the operating system, one through the browser, and one through Preview's export settings. The right method depends on how much reduction you need and how much quality you're willing to trade.
Method 1: Preview's Quartz Filter (Built-In, No Download)
Preview, the PDF viewer built into every Mac, can reduce file size through a Quartz filter. Open the PDF in Preview, go to File → Export, and in the Quartz Filter dropdown select "Reduce File Size." Save the file and you'll have a compressed version alongside the original.
The honest caveat: Preview's Reduce File Size filter is aggressive. It compresses images hard and can produce noticeably lower quality output, especially for photos. For a PDF that's mostly text, the result is usually fine. For a document with photographs or detailed graphics, the quality drop may be too much. Test on a copy before replacing the original.
Method 2: Export With Better Quality Settings
Preview's Export as PDF (different from the Quartz filter path) lets you control quality more precisely on some macOS versions. In File → Export as PDF, some Macs show image quality options. If your version supports it, choose a quality level between High and Low — Medium typically produces good results with meaningful size reduction.
This method produces cleaner output than the Quartz filter for image-heavy PDFs because you control the compression level rather than letting the filter apply a blanket reduction.
Method 3: Browser-Based Compression Tool
For the best balance of size reduction and quality, a browser-based PDF Compression tool outperforms Preview's built-in options. Open Safari or Chrome, go to WukongPDF, upload the PDF, choose your quality level, and download the compressed result. The tool applies smarter compression than Preview — lossless for text and vectors, optimized lossy compression for images only — which preserves visual quality better at comparable size reductions.
This method takes about a minute and works on any Mac without installing anything. For PDFs you need to keep looking good — client deliverables, professional documents, photos — the browser tool is the better choice over Preview's Quartz filter.
Method 4: ColorSync Utility for Advanced Control
Mac's ColorSync Utility (found in Applications → Utilities) lets you create custom Quartz filters with specific compression settings. Open the utility, go to Filters, duplicate the "Reduce File Size" filter, and adjust the image quality and resolution settings to something less aggressive than the default. Save your custom filter, then use it in Preview's export dialog. This gives you the no-upload convenience of Preview with more control over the output quality.
Which Method to Use When
For text-only PDFs where quality doesn't matter much: Preview's Quartz filter is fast and requires no browser. For image-heavy PDFs where quality matters: use a browser-based tool for better results. For confidential documents you'd rather not upload anywhere: the ColorSync custom filter approach keeps everything local. For any PDF over 5MB that needs to be emailed: try the browser tool first — the size reduction is almost always worth the 60 seconds.