How to Reduce PDF File Size on Mac (5 Free Methods)

Mac users have a surprising advantage when it comes to PDF compression: macOS ships with built-in tools that can shrink PDF files without installing a single extra app. Whether you are trying to email a 30 MB report, upload a document with a strict file size limit, or just free up some disk space, here are five free methods to reduce PDF file size on your Mac — ranging from dead simple to power-user territory.

Method 1: Use Preview's Built-In Compression

Preview is the default PDF viewer on Mac, and it has a hidden compression feature that most people never discover. This is the easiest method and works well for most documents.

Steps

Open your PDF in Preview. Double-click the file, or right-click and choose "Open With" then "Preview."
Go to File then Export. Do not use "Save" or "Save As" — you need "Export" for the compression options to appear.
Change the Quartz Filter. In the export dialog, look for the "Quartz Filter" dropdown menu. Select "Reduce File Size."
Choose a save location and click Save.

The compressed file will be significantly smaller — often 40-70% smaller depending on the content. The trade-off is image quality: photos and graphics in the PDF will be compressed noticeably. For text-heavy documents, this is usually fine. For presentations with high-res images, you might want a gentler approach.

Method 2: Create a Custom Quartz Filter

The built-in "Reduce File Size" filter is aggressive. It compresses images heavily, which can make your PDF look terrible if it contains photos or diagrams. The solution? Create your own custom Quartz filter with gentler settings.

Using ColorSync Utility

Open ColorSync Utility. Find it in Applications, then Utilities, or search with Spotlight (Cmd + Space).
Click the Filters tab. You will see the built-in filters including "Reduce File Size."
Duplicate the filter. Click the gear icon next to "Reduce File Size" and select "Duplicate Filter." Rename it to something like "Reduce File Size - Gentle."
Adjust the image compression settings. Expand the filter and modify the "Image Sampling" and "Image Compression" components. Try setting the sampling resolution to 150 DPI instead of the default 512 pixels, and use medium JPEG compression instead of low.
Save and use it. Your custom filter now appears in Preview's Quartz Filter dropdown when you export.

This gives you much more control over the quality-to-size trade-off. You can create multiple filters for different scenarios — one for email attachments, one for web uploads, one for archiving.

Method 3: Use an Online PDF Compressor

If you want more sophisticated compression without fiddling with Quartz filters, online tools offer smart compression that balances file size and visual quality better than Preview's built-in option.

Recommended Online Tools

PeacefulPDF: Upload your PDF, pick your compression level, and download the smaller version. Files are processed in your browser for privacy. No account needed, no watermarks.
iLovePDF: Offers three compression levels — extreme, recommended, and less. The recommended setting typically reduces file size by 50-60% with minimal visible quality loss.
Smallpdf: Clean interface with a basic compression option on the free tier. Good for quick one-off compressions.
PDF24 Tools: Completely free with no limits. Lets you choose DPI and image quality settings for granular control.

For sensitive documents, use PeacefulPDF or another tool that processes files locally in your browser rather than uploading them to a remote server.

Method 4: Compress via Terminal

For Mac power users who prefer the command line, you can use Ghostscript to compress PDFs with precise control over quality settings. This method requires installing Ghostscript via Homebrew.

Setup

Install Homebrew (if you do not have it): Open Terminal and paste the Homebrew install command from brew.sh.
Install Ghostscript: Run brew install ghostscript

Compression Command

Once Ghostscript is installed, use this command to compress a PDF:

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

The -dPDFSETTINGS flag controls the compression level:

/screen — Lowest quality, smallest file (72 DPI images)
/ebook — Medium quality, good balance (150 DPI images)
/printer — High quality (300 DPI images)
/prepress — Maximum quality (300 DPI, color profiles preserved)

This method gives you the most control and produces consistent, predictable results. It is also scriptable — you can batch-compress entire folders of PDFs with a simple shell script.

Method 5: Reduce PDF Size by Optimizing Content

Sometimes the best way to reduce file size is to address what is making the PDF large in the first place. Here are content-level optimizations that work regardless of which compression tool you use:

Remove unnecessary images: Embedded stock photos, decorative graphics, and duplicate images bloat file size. Remove or replace them with optimized versions.
Downsample high-res images: If your PDF contains 600 DPI images meant for screen viewing, downsample them to 150 DPI. Nobody will notice the difference on a screen, but the file size drops dramatically.
Flatten form fields: Interactive form fields, annotations, and comments add overhead. Flatten them into static content before compressing.
Remove embedded fonts (carefully): If the PDF uses standard fonts that are available on most systems, removing embedded fonts can save significant space. Only do this if you are sure the fonts will render correctly without embedding.
Delete unused pages: Blank pages, duplicate pages, or pages you do not need should be removed before compression. Every page adds to the file size.
Clean up metadata: Document metadata, revision history, and hidden layers can add surprising bulk. Strip them out before compressing.

Which Method Should You Use?

Here is a quick decision guide:

Need it done in 10 seconds? Method 1 (Preview Export) — fastest, built-in, no thinking required.
Need better quality control? Method 2 (Custom Quartz Filter) — takes 5 minutes to set up once, then reusable forever.
Compressing sensitive documents? Method 3 (PeacefulPDF online) — browser-based processing keeps your files private.
Compressing lots of files? Method 4 (Terminal + Ghostscript) — batch process entire directories from the command line.
Want maximum compression? Method 5 (Content optimization) plus any compression method — tackle the root cause and then compress.

Frequently Asked Questions

Does reducing PDF file size affect quality?

It depends on the method and settings. Aggressive compression reduces image quality noticeably. Gentle compression (150 DPI, medium JPEG) is usually indistinguishable from the original for on-screen viewing.

Can I reduce PDF file size on Mac without installing anything?

Yes. Method 1 (Preview Export) uses only built-in Mac software. Open the PDF in Preview, export with the "Reduce File Size" Quartz filter, and you are done.

How much can I reduce a PDF file size?

Text-heavy PDFs can often be reduced by 60-80%. PDFs with lots of high-res images typically see 40-60% reduction. The exact savings depend on the content and compression method.

Is there a file size limit for online PDF compressors?

Most free online tools have limits ranging from 5 MB to 100 MB per file. PeacefulPDF handles files up to a generous size limit. For very large files, the Terminal method with Ghostscript has no practical limits.

Can I undo PDF compression?

No. Compression is a one-way process. Always keep a copy of the original file before compressing. Preview's Export method naturally preserves the original since you are saving to a new file.