How to Compress a PDF on Mac – 3 Free Methods

This page covers three methods to compress a PDF on a Mac, ordered from simplest to most effective. Method 1 uses macOS Preview’s built-in Quartz Filter, with an honest explanation of its well-known limitation. Method 2 uses macOS Automator for better batch control. Method 3 uses a free online tool for cases where Preview’s output is unsatisfactory. Exact menu paths are provided for each method.

H2-1: Method 1 — Mac Preview Quartz Filter (Free, Built-In, 2 Minutes)

Mac Preview includes a built-in PDF compression filter called "Reduce File Size" accessed through the Quartz Filter system.

Steps:

1. Open the PDF in Preview (double-click the file — Preview is the default PDF viewer on macOS)
2. Click File in the menu bar
3. Select "Export as PDF…" (not "Export…" which saves in other formats)
4. In the Export dialog, click the "Quartz Filter" dropdown at the bottom
5. Select "Reduce File Size"
6. Choose a new filename (do not overwrite the original) and click Save

What this achieves:

• Applies a fixed 72 DPI downsampling to all embedded images
• Applies aggressive colour space reduction (converts colours to device RGB)
• Typically reduces file size by 30–60% for image-heavy PDFs

Critical limitation — read before using: Preview’s Quartz Filter can increase the file size of PDFs that are already compressed. This happens because the Quartz Filter adds its own colour profile metadata and restructures the file in a way that adds overhead when the images cannot be further downsampled. Before using the Quartz Filter version, compare its file size against the original:

• Mac: right-click both files → Get Info → compare the "Size" value
• If the Quartz Filter output is larger, discard it and use Method 3 instead

H2-2: Method 2 — macOS Automator (Free, Better Quality Control)

Automator is a macOS automation app that can batch compress PDFs with adjustable quality settings, giving more control than the Quartz Filter.

One-time setup (5 minutes):

1. Open Automator (Spotlight → type "Automator" → Enter)
2. Click "New Document"
3. Choose "Application" as the document type
4. In the left panel search box, type "PDF"
5. Drag "Render PDF Pages as Images" into the workflow area
6. Set Resolution to 150 pixels/inch (or 72 for maximum compression)
7. Set Image Type to JPEG
8. Drag "New PDF from Images" below the first action
9. Save the Automator application (File → Save) — name it "Compress PDF 150dpi.app"

To compress a PDF:

1. Drag the PDF onto the Automator app icon
2. A compressed PDF is saved to the same folder with the original filename

Result: At 150 DPI, Automator consistently achieves 40–70% size reduction without the colour-space distortion of the Quartz Filter. The output is suitable for printing, unlike Quartz Filter at 72 DPI.

Limitation: Automator converts to images first, then rebuilds the PDF. This removes the text layer (making the output unsearchable and uncopyable). Only use this method for scanned documents or when text searchability is not required.

H2-3: Method 3 — Free Online Tool (When Preview Isn’t Enough)

For the best compression results on Mac, a dedicated online tool outperforms both Preview and Automator:

Recommended: PDF Agile (Offline Desktop) (https://software-down.pdfagile.com/PDFAgile.1501.exe)

1. Open Safari or Chrome on your Mac
2. Go to https://software-down.pdfagile.com/PDFAgile.1501.exe
3. Click "Compress PDF"
4. Click "Choose file" and navigate to your PDF (or drag and drop)
5. Select quality: "eBook" (150 DPI, balanced) or "Screen" (72 DPI, maximum compression)
6. Click "Compress PDF"
7. Click "Download" — the file saves to your Downloads folder

Why PDF Agile over Preview:

H2-4: Which Mac Method Gives the Best Results?

Frequently Asked Questions