FileKitHow to Reduce PDF Size on Mac — Preview, Browser, and Command Line
Four methods for compressing PDFs on macOS — Preview built-in filter, browser tools, custom Quartz filters, and Ghostscript command line.
macOS Has Built-In PDF Compression
Mac users have a unique advantage: macOS includes a PDF compression filter in Preview and the ColorSync utility. No app downloads or subscriptions needed. But the built-in filter is aggressive — it downsizes images to 72 DPI, which can make text blurry. Here are all the options, from gentle to extreme.
Method 1: Browser-Based Tool (Best Balance)
For the best balance between size reduction and quality, use FileKit PDF Compressor in Safari or Chrome. It compresses the PDF structure and internal images without the harsh 72 DPI limit that Preview uses.
- Open FileKit in your browser
- Drag your PDF into the tool
- Select Balanced or Strong compression
- Download the compressed version
All processing happens locally — your files stay on your Mac.
Method 2: Preview (Built-In, Quick)
Open the PDF in Preview, then go to File > Export and select “Reduce File Size” from the Quartz Filter dropdown. This applies Apple's built-in compression filter.
Warning: This filter is aggressive. It downsamples all images to 72 DPI and can make photos and scanned text noticeably blurry. Only use this for documents that will be viewed on screen, not printed.
Method 3: Custom Quartz Filter (Advanced)
For more control, create a custom Quartz filter in ColorSync Utility:
- Open ColorSync Utility (Spotlight > “ColorSync Utility”)
- Go to the Filters tab and duplicate “Reduce File Size”
- Edit the duplicate — set Image Compression quality to 0.5-0.75 and resolution to 150 DPI
- Save with a descriptive name like “Medium Compression”
- Use this filter in Preview > Export > Quartz Filter
This gives you a reusable preset that compresses without destroying quality.
Method 4: Ghostscript (Command Line)
Install Ghostscript via Homebrew (brew install ghostscript) and run:
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 \
-dPDFSETTINGS=/ebook \
-dNOPAUSE -dQUIET -dBATCH \
-sOutputFile=compressed.pdf original.pdfUse /screen for maximum compression, /ebook for balanced, or /printer for print-quality output.
Comparison of Methods
| Method | Ease | Quality | Compression |
|---|---|---|---|
| FileKit (Browser) | Very easy | Good | 40-60% |
| Preview (Reduce) | Very easy | Low (72 DPI) | 60-80% |
| Custom Quartz Filter | Moderate | Customizable | 30-60% |
| Ghostscript | Technical | Customizable | 40-70% |
Related Tools
- General PDF Compression Guide
- How to Merge PDFs — merge first, then compress the combined file