How to compress a PDF on a Mac and reduce its file size

With PDF Unlimited (free)

1. Open the PDF

   Open the oversized file in PDF Unlimited.

2. Choose Export Compressed

   Choose File > Export Compressed…

3. Pick a preset

   Choose Low, Medium or High. The app shows the before and after size, so you can see whether it is worth it.

4. Save a copy

   Save the compressed version under a new name. Your original stays full quality.

5. Check it

   Open the new file and zoom in on small print and photos. If anything looks rough, export again with a gentler preset.

With Preview, built into macOS

1. Open Export

   Open the PDF in Preview and choose File > Export.

2. Choose the filter

   In the Quartz Filter pop-up menu, choose Reduce File Size.

3. Save under a new name

   Type a new name in Export As so you keep the original, then click Save.

Why some PDFs are huge

A PDF of pure text is tiny. The weight comes from images: scanned pages, phone photos of receipts, high-resolution charts, and embedded fonts. A 20-page scan saved at print resolution can easily run to tens of megabytes. That is the kind of file compression helps most.

If your PDF is mostly text and still large, it may contain embedded fonts or a single enormous image, like a logo exported at poster size. Compression helps less there.

Preview's Reduce File Size filter

Preview's built-in filter is free and quick, but it is blunt. It applies one fixed setting to every image, which can leave scans blurry and small print hard to read. On some files it barely helps. Depending on your macOS version, the Export sheet may also show extra image options you can try instead.

PDF Unlimited gives you three presets and shows the before and after size up front, so you can pick the gentlest setting that still fits under your email limit.

How to make a PDF smaller for email

Many email services cap attachments at around 20 to 25 MB, and upload portals are often stricter. A few tactics, in order:

• Try Medium first. It is the usual sweet spot for scans.
• Delete pages nobody needs, like blank backs of scanned sheets. See delete pages from a PDF.
• Split a long document into parts with split PDF and send them separately.
• Use High only for documents that will be read on screen, not printed.

What compression does not do

It will not remove passwords, change text, or strip annotations. Highlights and signatures survive. It also will not make a scan searchable; for that, run OCR before you compress.

Which preset to pick

Think about where the file is going. A document that will be printed or zoomed into, like a contract or a floor plan, deserves the gentlest setting that fits your limit. A document that will only be skimmed on a screen, like a scanned receipt for an expense report, can take stronger compression without anyone noticing.

You do not have to guess. The export window shows the before and after size, so try one preset, check the number, and move up or down. Keep the original until the compressed copy has been accepted.

Questions