The fastest way to compress a PDF on a Mac

The built-in Preview app on your Mac can compress a PDF in about 30 seconds without installing anything. Open the PDF in Preview, go to File > Export, choose your quality level from the Quartz Filter dropdown, and save. This works for most PDFs and reduces file size by 20 to 50 percent depending on the original content and quality setting you pick.

If Preview's built-in compression is not enough, or if you need more control over the process, macOS also includes a command-line tool called Automator that can batch-compress multiple PDFs at once. For files that contain mostly text, this method often shrinks them to a quarter of their original size.

The method you choose depends on how much smaller the file needs to be and whether you are compressing one PDF or many. Both approaches are free and do not require you to upload your file anywhere or sign up for an account.

Key Takeaways

  • Preview's Export function with Quartz Filter compression is the quickest method for a single PDF and takes less than a minute.
  • You can choose between four quality levels in Preview — from Maximum Quality down to Reduced File Size — depending on how much compression you need.
  • Automator can compress multiple PDFs in one batch operation, which saves time if you have many files to shrink.
  • Text-heavy PDFs compress much more than image-heavy ones, so results vary depending on what your PDF contains.
  • All compression happens on your Mac itself — your files never leave your computer.

Compress a single PDF using Preview

Open the PDF you want to compress by double-clicking it. It will open in Preview by default. If it opens in a different app, right-click the file, select "Open With," and choose Preview from the list.

Once the PDF is open in Preview, click the File menu at the top of the screen. From the dropdown, select "Export." A save dialog will appear with several options.

Look for the "Quartz Filter" dropdown menu in the export dialog. Click it and you will see four compression options: Maximum Quality, High Quality, Reduce File Size, and Reduce File Size (Even More). Start with "Reduce File Size" for most documents. If the file is still too large, you can repeat the process and choose "Reduce File Size (Even More)" the second time.

Give the file a new name if you want to keep the original, or use the same name to replace it. Click "Save" and the compressed PDF will be created. Check the file size by right-clicking the PDF, selecting "Get Info," and comparing the new size to the original.

Understand the quality trade-offs

Each Quartz Filter setting compresses differently. "Maximum Quality" makes almost no change to file size but keeps the PDF looking exactly as it was. "High Quality" removes some invisible data but the PDF looks the same to your eye. "Reduce File Size" removes more data and is noticeable only on PDFs with many high-resolution images. "Reduce File Size (Even More)" can make text slightly blurry on very large zoom levels, but most people will not notice at normal reading size.

Text-based PDFs (like scanned documents or forms) compress much more than image-heavy PDFs (like magazines or design files). A text PDF might shrink to 10 percent of its original size, while a photo-heavy PDF might only shrink to 60 percent. This is because text compresses easily, but images do not.

If you are emailing the PDF or uploading it somewhere with a file size limit, start with "Reduce File Size" and check the result. If it is still too large, repeat the export with "Reduce File Size (Even More)." You can always go back to the original if the quality is not acceptable.

Compress multiple PDFs at once with Automator

If you have many PDFs to compress, Automator can do them all in one batch. Open Automator by clicking the Spotlight icon (magnifying glass) in the top right corner of your screen, typing "Automator," and pressing Enter.

When Automator opens, select "New" and choose "Quick Action" from the dialog that appears. In the search box on the left, type "PDF" and look for the action called "Compress PDF." Drag it into the workflow area on the right.

In the Compress PDF action, set the Quartz Filter to the compression level you want. Then save the Quick Action with a name like "Compress PDFs." Once saved, you can right-click any PDF file, select "Quick Actions," and choose your compression action from the menu. It will compress the file and save it with "_Compressed" added to the filename.

To compress multiple files at once, select all the PDFs you want to compress in Finder, right-click, go to Quick Actions, and run your compression action. Automator will process them one after another without you having to do anything else.

When to use third-party tools instead

Preview and Automator handle most compression needs, but some situations call for a different approach. If you need to compress a PDF while keeping specific elements (like keeping images high-quality while shrinking text), or if you need to compress hundreds of files regularly, third-party tools like PDF Squeezer or PDFtk offer more control.

You would also want a third-party tool if you need to compress PDFs as part of a workflow with other file types, or if you need to compress PDFs on a schedule without opening Automator each time. These tools cost money but offer features that the built-in options do not.

For most people compressing one or a few PDFs, Preview is faster and does the job well enough. Only move to a paid tool if you find yourself compressing PDFs regularly and the built-in methods are not meeting your needs.

Troubleshoot compression that did not work

If your PDF did not get much smaller, the file probably contains mostly images or already-compressed content. Scanned documents and photos compress well; PDFs created from images or already-compressed files do not. There is no way around this — you cannot compress something that is already compressed without losing quality.

If Preview is not showing the Quartz Filter option, make sure you are using the Export function, not Save. Export is the only option that includes compression filters. Also check that you are running a recent version of macOS — very old Macs may not have all four compression levels available.

If the compressed PDF looks blurry or has missing text, you used too aggressive a compression setting. Go back to the original file and try again with "High Quality" or "Reduce File Size" instead of "Reduce File Size (Even More)."

Frequently Asked Questions

Can I compress a PDF without losing any quality?

Not significantly. "Maximum Quality" removes almost nothing, but it also barely shrinks the file. Real compression always trades some quality for file size. For most PDFs, "High Quality" or "Reduce File Size" is invisible to the human eye and cuts the file size by 30 to 50 percent.

Why did my PDF barely get smaller after compression?

PDFs that are mostly images or already compressed do not shrink much. Scanned documents and text-heavy PDFs compress well because text compresses easily. If your PDF is mostly photos or graphics, compression will not help much no matter which tool you use.

Can I undo a compression if I do not like how it looks?

Yes, as long as you saved the compressed version with a different name. Your original file stays unchanged. If you overwrote the original, you cannot undo it, so always keep a backup of important PDFs before compressing.

Does compressing a PDF change the content or make it unreadable?

No. Compression only removes data that makes the file smaller without changing what the PDF says or how it displays. The text and images will still be there and readable, though images may look slightly less sharp at very high zoom levels with aggressive compression.

Can I compress a password-protected PDF?

Preview can compress a password-protected PDF if you can open it. If the PDF is locked so you cannot edit it, compression will not work. You would need to remove the password protection first, which requires knowing the password.