How to Reduce the File Size of a PDF on Mac

Large PDFs are a common frustration — they clog up email attachments, slow down uploads, and eat into storage. The good news is that macOS has several built-in ways to compress PDFs, plus a range of third-party options depending on how much control you need. Understanding what's actually making your PDF large in the first place helps you choose the right approach.

Why PDF Files Get So Large

Not all PDFs are bloated for the same reason. A PDF's file size is shaped by what's inside it:

• Images — High-resolution photos embedded in a PDF are the most common culprit. A single uncompressed image can add several megabytes.
• Fonts — PDFs often embed full font files so they display correctly on any device. Multiple custom fonts add up.
• Layers and annotations — Design files exported to PDF sometimes carry hidden layers, comments, or form fields.
• Scanned pages — PDFs created by scanning physical documents are essentially image files per page, often enormous if scanned at high DPI.
• Metadata and thumbnails — Some PDF creators include preview thumbnails and extensive metadata that inflate the file unnecessarily.

Knowing what's inside your PDF matters because different compression methods target different sources of bloat.

Method 1: Use Preview (Built Into macOS) 🖥️

Preview is macOS's default PDF viewer, and it includes a built-in compression option through its export settings.

How to use it:

1. Open your PDF in Preview.
2. Go to File → Export as PDF.
3. Click the Quartz Filter dropdown and select Reduce File Size.
4. Save the file.

This method is fast and requires no extra software. However, it applies a blanket compression filter — it aggressively downsizes images, sometimes reducing them to a lower quality than you'd want. For PDFs that are text-heavy with minimal graphics, results are usually fine. For photo-heavy documents, the quality loss can be visible.

A common workaround: macOS lets you create custom Quartz filters through ColorSync Utility, where you can set your own image resolution threshold (for example, downsampling images to 150 DPI instead of the default lower setting). This gives you more control over the quality-to-size tradeoff.

Method 2: Print to PDF (Sometimes Strips Extras)

Another native option is using the Print dialog to re-export:

1. Open the PDF in Preview.
2. Go to File → Print.
3. Click PDF → Save as PDF in the bottom-left corner.

This doesn't apply compression in the same way, but it can strip certain embedded extras like annotations, hidden layers, or unnecessary metadata — occasionally producing a noticeably smaller file.

Method 3: Use Third-Party PDF Editors or Compressors

For more precise control, third-party tools offer settings that macOS's built-in options don't.

Desktop editors like PDF editors available on the Mac App Store typically let you set image resolution targets (e.g., 72, 96, 150, or 300 DPI) and choose between lossy and lossless compression. This matters if you're compressing a PDF that will be printed versus one shared digitally — print usually requires higher resolution.

Online tools upload your file to a remote server, apply compression, and return the result. They're convenient but raise a consideration: if your PDF contains sensitive information, uploading it to a third-party server is a privacy decision worth thinking through deliberately.

Ghostscript is a free, open-source command-line tool that runs on Mac (installable via Homebrew) and gives expert-level control over compression settings. It's not beginner-friendly, but it's powerful for batch compression or when fine-tuning quality settings matters.

What Affects How Much You Can Compress

Several variables determine how much file size reduction is actually achievable:

• Original content type — A text-only PDF from a word processor might compress minimally because it's already efficient. A scanned document at 600 DPI can often be reduced dramatically.
• Acceptable quality threshold — Compressing images from 300 DPI to 72 DPI produces a tiny file but may look poor when zoomed in or printed. Compressing to 150 DPI is often a reasonable middle ground for screen viewing.
• macOS version — The Quartz filter behavior in Preview has changed across macOS versions. What works on one version may behave differently on another.
• PDF version and structure — Older PDF formats or those created by non-standard tools sometimes respond differently to compression utilities.
• Intended use — A PDF going to a printer needs to retain image quality. One being attached to an email or posted on a website can tolerate more aggressive compression.

The Spectrum of Use Cases

A student compressing a scanned assignment to email a professor has very different needs from a graphic designer compressing a portfolio PDF to share with clients. The first person probably cares only about getting under an email attachment limit and can tolerate quality loss. The second needs images to remain sharp and color-accurate.

Similarly, someone compressing one PDF occasionally will probably find Preview's built-in filter sufficient. Someone processing dozens of PDFs regularly — say, in a small business workflow — will likely hit its limitations quickly and benefit from a dedicated tool or automated script. 🔍

The right method also shifts depending on whether the PDF is editable or locked, whether it contains form fields you want to preserve, and whether the compression needs to be lossless (no data removed) versus lossy (smaller file, some data discarded).

What your specific PDF contains, how much quality loss is acceptable, and how often you need to do this all shape which approach will actually work well for you.