You open a PDF, check the file size, and see 18 MB. You need it under 5 MB to upload it somewhere, and you do not want to install any software. Your Mac already has Preview, ColorSync Utility, and a few other built-in tools. Can those tools, the ones Apple gave you for free, shrink a PDF down to size without making it look terrible?
The answer is yes, with some important caveats. macOS includes several built-in ways to reduce PDF file size, and the best method depends on what kind of content is inside your PDF. The tools are free, pre-installed, and require no downloads or accounts. But they each work differently, and using the wrong one can produce a file that looks noticeably worse than the original.
Method 1: Preview's Quartz Filter (The Quickest Method)
Preview, the default PDF viewer on every Mac, includes a built-in file size reduction feature that works through macOS's Quartz rendering engine. Open the PDF in Preview. Go to File, then Export. In the export dialog, click the Quartz Filter dropdown menu. Select "Reduce File Size." Choose a destination and click Save.
What this filter does is straightforward and aggressive. It resamples all images in the PDF to approximately 96 DPI and applies JPEG compression to them. For a text-heavy scanned document, this can reduce file size by 60% to 80%. The trade-off is that image quality degrades noticeably at this resolution. Small text in scanned pages may become difficult to read. Photographs will look soft and may show compression artifacts.
This method works best when you need a quick, rough Reduce PDF Size and image quality is secondary. An internal office memo scanned at 600 DPI can be dropped to a perfectly readable 1 MB file. A photo-heavy brochure will not fare as well. Preview's Reduce File Size filter is a blunt instrument. It applies the same settings to every image regardless of content. You get one level of compression and one output resolution, period.
Method 2: ColorSync Utility (More Control Over Image Compression)
ColorSync Utility, found in Applications, Utilities, is a less obvious but more flexible tool for PDF compression. Open ColorSync Utility, then open your PDF in it. At the bottom of the window, click the Filter dropdown and you will see a list of Quartz filters including "Reduce File Size" and possibly others you or your applications have added. More importantly, ColorSync Utility lets you create your own custom filters with specific compression settings.
To create a custom filter, open ColorSync Utility, go to the File menu, and choose Open, then navigate to /System/Library/Filters. You can duplicate an existing filter like "Reduce File Size" and edit its properties: change the image resolution from 96 DPI to 150 DPI for better quality, switch from JPEG to JPEG2000 compression for more efficient encoding, or add a color conversion step if your document has embedded color profiles you want to strip. Custom filters appear in Preview's Export dialog and in ColorSync Utility's Filter menu, so you can reuse them for future files.
This approach gives you the control that Preview's default filter lacks. For a scanned document where text legibility is important, a custom filter with 150 DPI output is a good compromise: file size drops by roughly 40% to 50% while text remains sharp. For a photo book where image quality matters, 200 DPI with moderate JPEG quality preserves the visual experience while still trimming the file to emailable size.
Method 3: Print to PDF (Strips Hidden Data and Redundant Objects)
The macOS print dialog includes an option to save any document as a PDF. This is normally used to create PDFs from other file types, but it also works on PDFs themselves. Open the PDF in Preview, choose File, then Print. In the print dialog, click the PDF button in the lower-left corner and choose "Save as PDF." Save the file with a new name.
This process, sometimes called refrying a PDF, forces macOS to completely re-render the document and write out a new PDF file from scratch. In doing so, it strips out several categories of bloat: unused objects left over from incremental saves, redundant font subsets, obsolete metadata entries, and shell structures from the original creation software. The visual output is identical to the original. The file size reduction is moderate, typically 10% to 25%, but it comes with no quality loss whatsoever because no image data is being resampled or recompressed.
For PDFs where the bloat comes from inefficient file structure rather than oversized images, this method is ideal. A contract generated by a legal document system might be 5 MB when it should be 200 KB. Print to PDF strips the overhead and produces a clean, compact file. It is also the safest method because it never degrades image quality. If the file is still too large after refrying, you know the bloat is in the images themselves, and you need to use a method that actually compresses image data.
Method 4: Create a Custom Automator Quick Action (For Repeated Use)
If you find yourself reducing PDF file sizes regularly, macOS Automator can turn any of the methods above into a one-click Quick Action that appears in Finder's right-click menu. Open Automator, create a new Quick Action, set it to receive PDF files in Finder, and add the "Apply Quartz Filter to PDF Documents" action. Choose your preferred filter, including any custom filter you created in ColorSync Utility. Save the Quick Action with a descriptive name like "Compress PDF for Email."
Once saved, you can right-click any PDF in Finder, scroll to Quick Actions at the bottom of the menu, and select your custom compression action. The compressed file is created instantly in the same folder. There is nothing to open, no dialog to navigate, and no settings to adjust. For anyone who processes multiple PDFs in a typical workday, this small automation investment pays for itself within the first week. These four methods cover most everyday needs. They share the same ceiling, though: none of them give you fine control over output quality.
When Built-In Tools Are Not Enough
When you need more than basic size reduction, the built-in macOS tools start to show their limits. None of them can selectively compress only the images while leaving text and vector graphics untouched at their original quality. None of them offer a preview of what the compressed file will look like before you commit. None of them let you adjust the compression level per image or per page. And none of them produce a side-by-side comparison of the original and compressed files.
For a file where image quality genuinely matters, a photo portfolio, a product catalog, a design presentation, the built-in tools can feel blunt. This is where a dedicated PDF Compression tool like WukongPDF earns its place. Unlike Preview's single aggressive filter, a compression tool designed for PDFs gives you control over the output quality, lets you see the result before downloading, and often produces better compression ratios at the same visual quality because the compression engine is tuned specifically for PDF image data rather than being a general-purpose Quartz filter shared across all macOS image operations.
The built-in tools are always available, require zero setup, and work offline. They are the right first stop for anyone on a Mac who needs to shrink a PDF. When they produce a result that is good enough, you are done in seconds. When they do not, you know exactly what you need from a more capable tool.