How to Reduce PDF File Size on Mac (Free, No New Apps)

A PDF that ballooned in size can stop you cold — an email bounces, an upload portal rejects the file, or a colleague cannot download an attachment. On a Mac you have two good paths to reduce the file size: the built-in Preview app, and a browser-based compressor. Both are free and require no new software.

This guide shows you both approaches, and explains when each is the better choice.

Why are my PDFs so large on a Mac?

• Scans saved at high resolution (300 DPI or more) carry a huge image payload
• Full-colour photos and graphics resist compression
• Embedded fonts, layers, and metadata add overhead
• Exporting from Pages, Numbers, or Keynote can leave generous image settings on

Method 1: Reduce the PDF size with Preview

1. 1Open the PDF in Preview on your Mac.
2. 2Click File, then Export (or File > Export as PDF).
3. 3Open the Quartz Filter menu and choose Reduce File Size.
4. 4Click Save to produce a smaller copy of the PDF.
5. 5Check the new file size — if it is still large, you may want a stronger option.

The Reduce File Size filter works well for text-based PDFs and lightly-scanned pages. For heavy colour scans it may barely budge the size, which is when a browser compressor that re-encodes images helps more.

Method 2: Compress with a browser tool

A browser-based compressor gives you control over how much to shrink the file, and it runs locally so your document never leaves your Mac:

1. 1Open the Compress PDF tool in any browser on your Mac.
2. 2Drag your large PDF into the upload area.
3. 3Choose how aggressively you want to compress — light, for crisp quality, or more, for the smallest possible file.
4. 4Click compress and download the smaller PDF.

You can compress as much as you need, then verify the result still looks readable before sending it.

Before you compress: clean up the source

If even heavy compression does not get the file small enough, the fastest win is usually at the source. Delete pages you do not need, remove large inserted images, and for scanned documents, avoid re-printing: re-scan at a lower DPI and in grayscale to dramatically cut size without hurting legibility. Compressing then becomes the final polish rather than a battle.