How to Compress a PDF on Mac

Mac users have several options for compressing PDFs — built-in tools in macOS (Preview and ColorSync), dedicated apps, and browser-based tools. Each method has different strengths, and the best choice depends on how much compression you need, whether quality loss is acceptable, and whether you want to install additional software. This guide covers all the main approaches available on Mac, with honest assessments of each.

Method 1: Preview's "Reduce File Size" Quartz Filter

macOS Preview has a built-in compression option via a Quartz filter called "Reduce File Size." It's quick to access but produces notoriously poor results — the filter aggressively degrades image quality in ways that are very visible at any print or close-screen inspection. Here's how to use it anyway, in case your file doesn't have images and you just want to remove metadata overhead: Step 1: Open the PDF in Preview. Step 2: Go to File → Export. Step 3: In the Quartz Filter dropdown, select "Reduce File Size." Step 4: Click Save. This applies a blanket quality reduction that works for some use cases (non-visual PDFs, rough drafts) but is generally not recommended for anything containing photographs, charts, or crisp graphics. The Preview filter is known for making images look blurry and text jagged in ways that are hard to recover from. Use it only when you have no better option and quality doesn't matter.

Method 2: ColorSync Utility (Customizable Quality)

macOS includes ColorSync Utility, which lets you create custom Quartz filters with more control over compression quality — a significant improvement over Preview's blunt "Reduce File Size" filter. Step 1: Open ColorSync Utility (find it in Applications → Utilities, or search with Spotlight). Step 2: Go to Filters tab → click the + button to add a new filter. Step 3: Name the filter (e.g., "PDF Compress Medium"). Step 4: Click the dropdown (▼) on the new filter and choose "Add Image Effects Component." Step 5: In the Image Sampling section, set Scaling to 50% and Image Quality (JPEG) to the desired level (70–85 is typically a good balance). Step 6: Close ColorSync Utility. Your new filter now appears in Preview's Quartz Filter dropdown. This gives much better quality control than the default Reduce File Size filter.

Method 3: Browser-Based Compression (Recommended)

For most Mac users who need reliable compression without quality surprises, a browser-based tool like PDF Mate is the best choice. It gives you three clearly defined quality levels with size preview before download, processes files locally in your browser (no upload), and produces consistently good results. Step 1: Open Safari or Chrome. Step 2: Go to pdfmate.io/tools/compress. Step 3: Upload your PDF (drag from Finder onto the browser window). Step 4: Choose Low, Medium, or High compression. Step 5: The tool shows the resulting file size before you download — if it's not small enough, try a higher level. Step 6: Download the compressed PDF. No software installation, no quality mystery, full transparency on results before committing.

Method 4: Ghostscript (Terminal — Power Users)

Ghostscript is a command-line PDF processing tool available on Mac via Homebrew. It offers the finest control over compression settings but requires comfort with the Terminal. After installing Homebrew and then Ghostscript (`brew install ghostscript`), you can run: `gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf`. The `-dPDFSETTINGS` option controls quality: `/screen` (lowest, 72 DPI), `/ebook` (medium, 150 DPI), `/printer` (high, 300 DPI), `/prepress` (highest, 300 DPI with full color). For most compression needs, `/ebook` is appropriate.

Comparing the Methods

Preview "Reduce File Size": Fast, no setup, but poor image quality. Only use for text-only PDFs or rough drafts. ColorSync custom filter: Better quality control than Preview, but requires one-time setup and still produces variable results. Browser-based (PDF Mate): Best balance of quality, convenience, and transparency. Recommended for most users. Ghostscript: Maximum control and often best quality results, but requires Terminal comfort. Best for batch processing or very specific quality requirements.

Tips for Mac PDF Compression

Check the file size difference before and after. Right-click the compressed file in Finder and Get Info to see its size. Compare to the original. If the reduction isn't substantial (less than 20%), the file was already well-optimized and aggressive compression will cause quality loss without proportionate size savings.

For images-heavy PDFs, browser-based tools outperform Preview. The WebAssembly PDF engines in browser tools (like PDF Mate) handle JPEG image recompression more intelligently than macOS's Quartz filter, producing better-looking results at smaller file sizes.

Keep the original. Always keep the uncompressed original. If the compressed version turns out to have worse quality than needed, you can compress again from the original with a lighter setting.

Frequently Asked Questions

Why does Preview's "Reduce File Size" make my images look terrible?
Preview's built-in Quartz filter uses very aggressive image downsampling (reducing resolution to 72 DPI) and low JPEG quality — far below what's needed for any visual content. It's a legacy tool that predates modern approaches to PDF optimization.

Can I compress PDFs in bulk on Mac?
Using Ghostscript in a shell script, yes — you can process many files automatically. For GUI-based batch compression, dedicated apps like PDF Squeezer (paid) or Smallpdf desktop (subscription) handle batch operations. Browser-based tools are generally one file at a time.

Does Mac's built-in compression support PDF/A output?
No — Preview's compression doesn't produce PDF/A-compliant output. For PDF/A compression, use Adobe Acrobat or a dedicated PDF/A tool.

Will compressed PDFs open normally in older macOS versions?
Yes — PDF compression doesn't change the PDF specification version. Compressed PDFs open in all versions of Preview and any other PDF viewer.

Compress PDFs on Mac at pdfmate.io/tools/compress — better results than Preview's built-in filter, completely free.