Mac has better built-in PDF tools than Windows, and reducing PDF size on a Mac without degrading quality is genuinely achievable — if you use the right method. The key is understanding what's causing the large file size in the first place, then targeting that specifically.
Why Some PDFs Are Large on Mac
PDFs exported from Mac applications are sometimes surprisingly large because of how macOS handles graphics. PDFs created by printing from Safari, Pages, or Keynote often embed image data at very high resolution, include color profile data, or embed full fonts even when a subset would do. A single-page document can end up at 10 MB or more for reasons that have nothing to do with the amount of visible content.
Using Preview's Quartz Filter to Reduce PDF Size
Mac's Preview app includes a built-in compression option called Reduce File Size. Open the PDF in Preview, go to File > Export, and select Reduce File Size from the Quartz Filter dropdown. Click Save.
This method is quick and convenient but applies aggressive compression — it often degrades image quality noticeably, downsampling images to 72 DPI regardless of the original resolution. For documents with important images or fine detail, the result is frequently too blurry to use professionally. It's best reserved for quick sharing where visual quality isn't critical.
Getting Better Results With an Online Tool
For better quality control, WukongPDF's PDF Compression tool gives you more nuance than Preview's blunt filter. Upload the file from Safari, choose a compression level that balances size and clarity, and download the result. The tool targets image data intelligently and preserves text and vector graphics at full sharpness regardless of compression level.
This approach typically produces a file that's 60–80% smaller than the original while remaining visually indistinguishable from it at normal viewing sizes — a much better outcome than Preview's Reduce File Size option for documents that contain photographs, charts, or fine text.
Using Ghostscript on Mac for Precise Control
For users comfortable with the terminal, Ghostscript offers precise control over PDF compression parameters. Install it via Homebrew with brew install ghostscript, then run a command specifying the image DPI, compression type, and output quality. This gives you fine-grained control that neither Preview nor most online tools can match.
A typical Ghostscript compression command sets the PDF compatibility level, image downsampling resolution, and JPEG quality in a single line. The ebook setting targets 150 DPI images at high quality — a good default for documents that need to look good on screen without being unnecessarily large.
Creating a Custom Quartz Filter for Better Results
Mac power users can create a custom Quartz filter through ColorSync Utility that targets 150 DPI instead of Preview's default 72 DPI. Open ColorSync Utility from Applications > Utilities, go to Filters, duplicate the Reduce File Size filter, and change the image sampling values. The new filter then appears in Preview's Export dialog alongside the built-in options.
This one-time setup takes about five minutes and gives you a PDF Compression option directly in Preview that produces much better image quality than the default filter — useful if you compress PDFs regularly and prefer to stay within Mac's built-in tools rather than using a browser-based option.