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How to compress a PDF on a Mac without making it blurry

Preview's Reduce File Size treats every picture the same way, so scans turn to mush. What it really does, a better free setting, and the one click way.

You export a PDF with Preview's Reduce File Size, it gets much smaller, and the text in it is suddenly hard to read. That is not bad luck. The filter applies one fixed rule to every picture in the file, and a scanned page is nothing but a picture.

The free way: Preview

  1. Open the PDF in Preview.
  2. Choose File > Export.
  3. Set Quartz Filter to Reduce File Size.
  4. Save under a new name, so the original stays as it was.

Why the result looks blurry

The filter is a small settings file at /System/Library/Filters/Reduce File Size.qfilter. Read on macOS 26.6.2 on 1 October 2026, it re-encodes every image as a JPEG at quality 0.7, scaled to 144 pixels per inch, and caps any image at 2,400 pixels on its longest side.

For a photo in a brochure that is often fine. For a scanned contract it is not, because every letter on the page is part of the image, and JPEG smears the sharp edges letters are made of. You can read the settings yourself:

plutil -p "/System/Library/Filters/Reduce File Size.qfilter"

A better free setting

ColorSync Utility, in Applications > Utilities, can make your own filter. Open its Filters window, duplicate Reduce File Size, and raise the image resolution and quality. Your copy then appears in Preview's Quartz Filter menu. It is still one rule for every picture, so expect to try a couple of settings per document.

The one click way

Simply PDF shrinks each picture to the size it is actually shown at on the page, so a small logo and a full page scan are treated differently, and it leaves text and drawings alone. Before you save, it shows the new size and a close up of the sharpest part of the page, so you see the blur before anyone else does.

Whatever you use, save a copy rather than overwriting. A compressed PDF cannot be un-compressed.

Questions

Why does Preview make my PDF blurry?

Its Reduce File Size filter turns every image into a JPEG at the same resolution and quality. On a scan, the text is part of the image, so it gets blurred along with everything else.

Can I compress a PDF on a Mac without uploading it?

Yes. Preview, a custom ColorSync filter and Simply PDF all work on your Mac. Online compressors upload the file to a server first.

Does compressing a PDF remove the text?

It should not. Text in a normal PDF is not an image and survives compression. Text in a scan is part of the image, which is why scans suffer most.

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