Mac users have several options for compressing PDFs — some built right into macOS, others available through free online tools. The results vary significantly depending on which method you use. Preview's built-in compression, for example, is convenient but produces inconsistent results. A dedicated compression tool using Ghostscript will typically reduce the file size by 40 to 80% compared to Preview's 10 to 20%.
Method 1 — Free online tool (best results)
The most effective free method on any device:
- Open Filero's free Compress PDF tool in Safari or Chrome.
- Upload your PDF.
- Choose a quality preset — Balanced works well for most documents.
- Download the compressed PDF.
Filero uses Ghostscript compression which typically reduces file size by 40 to 80%. This is significantly better than Preview's built-in Quartz filter. No account needed, nothing installed, and the file is never stored.
Method 2 — Preview (built-in, convenient)
Preview is the easiest option since it is already on your Mac:
- Open the PDF in Preview.
- Go to File > Export as PDF.
- Click the Quartz Filter dropdown and select "Reduce File Size".
- Save the file.
The limitation: Preview's Reduce File Size filter is aggressive on image quality and inconsistent on how much it actually compresses. For text-heavy PDFs it may barely reduce the size at all. For image-heavy PDFs it can make images look noticeably worse. It is fine for a quick rough reduction but not reliable for professional use.
Method 3 — Automator (batch compression)
If you need to compress multiple PDFs at once, Automator — also built into Mac — can handle it:
- Open Automator (search in Spotlight).
- Create a new workflow and choose "Application".
- Add the "PDF: Apply Quartz Filter to PDF Documents" action.
- Select "Reduce File Size" as the filter.
- Save the Automator application, then drag and drop PDFs onto it to compress them.
Same quality limitations as Preview, but useful for processing many files at once without opening each one individually.
Which method gives the smallest file size?
In order of effectiveness:
- Filero (Ghostscript): 40 to 80% reduction — best results
- Adobe Acrobat: 40 to 75% reduction — comparable to Ghostscript, paid
- Preview (Quartz filter): 10 to 30% reduction — inconsistent
For most people, the free online tool gives the best results with the least effort. Preview is fine if the PDF is already small and you just need a slight reduction.
Frequently asked questions
Why is my PDF so large on Mac?
The most common cause is embedded images. PDFs created from Word documents with photos, from InDesign layouts, or from scanned documents can be very large because the images inside are stored at full resolution. Compression reduces the image resolution to a level that is still good for screen viewing but takes far less space.
Will compressing a PDF reduce the text quality?
No — text in a PDF is stored as vector data, not as an image. Compression only affects the embedded images. Text always remains sharp regardless of compression level.
What is the best PDF compression setting for emailing?
The Balanced preset in Filero (150 DPI) is ideal for emailing. It reduces file size significantly while keeping images looking good on screen and when printed on a standard printer. The Small preset (72 DPI) gives the smallest file but images may look soft if printed.
Ready to try it?
Use Filero's free Compress PDF tool. No account needed, works on any device.
Open Compress PDF