3 Ways to Compress a PDF on Mac
Method 1: PDF.it Online (Recommended)
Best results. Three compression levels with predictable, controllable output.
- 1. Open Safari → go to pdf.it.com/compress-pdf
- 2. Upload your PDF
- 3. Choose Light, Medium, or Extreme
- 4. Download the compressed PDF
No install needed. Works on any Mac, any macOS version.
Method 2: Preview (Built-in — Inconsistent Results)
Available on every Mac, no internet required. But results are unpredictable — sometimes increases file size.
- 1. Open the PDF in Preview
- 2. File → Export as PDF
- 3. Click the Quartz Filter dropdown
- 4. Select "Reduce File Size"
- 5. Click Save
Note: This filter often produces poor quality or even larger files on already-optimized PDFs.
Method 3: Automator (For Batch Compression)
Good for compressing many PDFs at once automatically. Uses the same Quartz filter as Preview.
- 1. Open Automator (in Applications)
- 2. Create a new Workflow
- 3. Add "Get Specified Finder Items" → add your PDFs
- 4. Add "PDF: Filter PDF Documents" → choose Reduce File Size
- 5. Run the workflow
Method Comparison
| Method | Size Reduction | Quality Control | Internet Needed |
|---|---|---|---|
| PDF.it | Excellent | 3 levels | Yes |
| Preview | Variable | None | No |
| Automator | Variable | None | No |
Why Preview's "Reduce File Size" Often Fails
Apple's built-in Quartz filter works by re-encoding the entire PDF — including content that's already efficiently compressed. This re-encoding process:
- • Can increase the file size if the original is already well-compressed
- • Degrades image quality more aggressively than necessary
- • Doesn't offer quality control — you get one result with no adjustment
For consistent, predictable results, PDF.it compresses only what needs compressing and lets you choose the quality trade-off.