How to Compress a PDF on Mac

Mac has two built-in ways to shrink a PDF: Preview's Quartz filter and the Export as PDF option. For most people, a free browser tool like CalmPDF is faster and more predictable — no Quartz filter required, and your file never leaves your device.

Method 1: Compress using Preview

Preview is built into every Mac and can reduce PDF size using Apple's Quartz compression filter. The result is often quite aggressive — good for file size, but it can noticeably soften images.

1. Open the PDF in Preview (double-click it in Finder).
2. Go to File → Export as PDF.
3. Click the Quartz Filter dropdown and choose Reduce File Size.
4. Save the file with a new name.

This can cut file size by 50–80%, but the Quartz filter was designed for print workflows, not the web. Images may lose sharpness, and occasionally text rendering changes. For documents you share professionally, preview the result before sending.

Method 2: Export from Preview (lighter touch)

If Reduce File Size is too aggressive, try a plain export without the Quartz filter:

1. Open the PDF in Preview.
2. Go to File → Export as PDF.
3. Leave the Quartz Filter set to None.
4. Save. Preview re-encodes the PDF, which sometimes removes metadata bloat and shrinks the file slightly without quality loss.

Method 3: Use CalmPDF (browser-based, private)

CalmPDF runs entirely in your browser. You don't install anything, and your PDF is never uploaded to a server — useful if the document contains sensitive information.

1. Open calmpdf.com/compress-pdf in any browser.
2. Drop your PDF into the upload area.
3. Choose a compression level — High quality keeps images crisp;Smaller file reduces size more aggressively.
4. Click Compress and download the result.

CalmPDF works on any Mac (Intel or Apple Silicon) without installing software or creating an account. It works on Safari, Chrome, Firefox, and Edge.

Which method should you use?

Use Preview's Quartz filter if you want a fully offline solution and don't mind some image quality loss — it's fast and built into macOS.

Use plain Export if you have a text-heavy PDF that's larger than it should be due to metadata or structure overhead.

Use CalmPDF if you need predictable results, want to compare compression levels side by side, or are working with confidential documents that shouldn't be uploaded to cloud services.

Why are PDFs large in the first place?

Most large PDFs are image-heavy — think scanned documents, presentation exports, or forms with embedded photos. Each image is stored at full resolution by default. Compression resamples those images at a lower resolution, which dramatically reduces file size with minimal impact on on-screen readability. Text-only PDFs are usually already small and compress less.

Frequently asked questions

Does compressing a PDF reduce quality?

It depends on the method. The Quartz filter in Preview is lossy and can soften images. CalmPDF's high-quality preset is designed to preserve readability while still reducing size. Text in PDFs is vector-based and is never affected by image compression.

Is there a size limit for PDF compression on Mac?

Preview has no enforced size limit, but very large PDFs (500 MB+) can be slow. CalmPDF's limit is determined by your browser's memory — most laptops handle up to 200 MB comfortably.

Can I compress a PDF on a Mac without the Quartz filter?

Yes. Use the plain Export method (no Quartz filter selected), or use CalmPDF which applies its own compression algorithm without the Quartz filter's side effects.