Why Preview makes a PDF bigger

Preview’s “Reduce File Size” filter uses one fixed setting for every PDF, and it doesn’t check that the result is smaller. So a PDF whose pictures were already compressed can come out bigger, and one with detailed photos comes out blurry.

What the filter does

File → Export → Quartz Filter → Reduce File Size saves a new copy of the PDF with its pictures made smaller and saved again. The filter has no options in Preview: the same setting is used for a scanned contract, a photo brochure and a text-only report, and Preview saves whatever comes out.

What you can do instead

Keep the original and compare: if the copy is bigger or blurry, don’t use it.
Make your own filter with a different setting in ColorSync Utility (in Applications → Utilities); Preview lists it under Quartz Filter.
Whizra: select the PDF and type compress it. You pick strong, good or light (or say for email), text stays selectable, and if the result isn’t at least 5% smaller it says so and keeps nothing.

Questions

Why is my PDF blurry after Reduce File Size?

The filter makes every picture smaller with one fixed setting, whatever the PDF is. Detailed photos lose sharpness.

Why is my PDF bigger after Reduce File Size?

Preview doesn’t check that the new file is smaller. A PDF whose pictures were already compressed can come out bigger.

Is there a free way with better control?

Yes: make your own Quartz filter in ColorSync Utility, or compare a few settings. Whizra gives three qualities and never keeps a result that isn’t smaller.

Checked: 3 Nov 2026.

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