PDFs and conversion
How to compress a PDF on a Mac and reduce its file size
Compress a PDF on a Mac for free with Preview, make a gentler filter in ColorSync Utility, or let Orrel try three levels and keep only a result that is actually smaller.
Email services and upload forms often cap attachments, and PDFs made from scans or phone photos sail past the limit. macOS can shrink a PDF without any extra software; the question is how much quality you are willing to give up.
Preview's Reduce File Size
- Open the PDF in Preview.
- Choose File › Export. Not Export as PDF: that dialog has no filter option.
- Give the copy a new name so the original is kept.
- Open the Quartz Filter menu and choose Reduce File Size.
- Click Save, then compare the two sizes in Finder.
Apple notes the result may be lower quality than the original, and in practice the built-in filter is blunt. It downsamples images heavily, which is fine for a receipt and noticeably poor for a photo or a page of small print. Always open the copy and zoom in before sending it.
A gentler filter with ColorSync Utility
The Quartz filters Preview offers are defined in ColorSync Utility, in Applications › Utilities. Open it and click Filters in the toolbar. Find Reduce File Size, open the menu at the right of its row and choose Duplicate Filter. Expand the copy and adjust its Image Sampling and Image Compression settings: a larger maximum size or a higher quality keeps more detail. Rename the copy so you can tell them apart.
Your copy then appears in Preview's Quartz Filter menu. It takes some trial and error to find settings that suit your documents, but you only do it once.
Other things that make PDFs large
- Scans at high resolution. Rescanning at 200 to 300 dpi in greyscale is often smaller than compressing a 600 dpi colour scan.
- Photos dropped into a document. Resize images before putting them into a word processor.
- Embedded fonts and duplicates. Merging several PDFs can include the same font many times. Little can be done about this without specialist tools.
How Orrel does it
Orrel's Compress offers three levels, Balanced, Smaller and Smallest, and at each one tries several methods rather than one. That includes a Quartz filter tuned for the level, re-compressing the images inside the PDF, and at Smallest, turning each page into a JPEG image. It keeps whichever result is smallest and tells you the before and after sizes.
- Only saved if it helps. A result is written only when it is at least 5% smaller than the original. If nothing helps, nothing is saved and Orrel says so.
- New file, original kept. The compressed PDF is saved beside the original, never over it.
- From anywhere. Compress from the PDF workspace after a merge, from the right-click menu, or by asking a connected AI assistant.
Where Orrel stops
Some PDFs are already compact, and no level makes them meaningfully smaller; Orrel reports that rather than saving a near-identical copy. The Smallest level turns pages into images, which suits scans but means the text is no longer selectable or searchable, and fine print becomes softer. Use Balanced for contracts and anything someone will need to copy text from. Orrel does not remove embedded fonts or edit the document's structure.
Questions
Why did Preview make my PDF larger?
Re-saving through macOS can re-encode images less efficiently than the app that made the PDF. Exporting without a Quartz filter, or with a filter that does not suit the file, can produce a larger file. Compare the sizes before you replace the original.
Why is my text blurry after compressing?
Some methods turn each page into a picture. That shrinks scans well but makes text a little soft and no longer selectable. Use a gentler level for documents that are mostly text.
How small can a PDF get?
It depends on what is inside. Scans and photo-heavy PDFs often shrink a lot. A text-only PDF made by a word processor may already be about as small as it can be.