How to Compress PDF on Mac

A 40-slide deck can be 30 MB even though the text is light. The slide images inside the PDF carry the weight. You notice when email bounces, a client portal rejects the upload, or a shared drive link takes forever to open. The fix is usually shrinking embedded images, not deleting content. A single aggressive filter pass can blur charts; a measured re-export from the source deck often keeps text sharp while still fitting upload limits.

Why PDFs get large

Most PDF bloat comes from raster images saved at print resolution inside a file meant for screen viewing. Text and vector shapes stay small; photos, slide exports, and scans dominate the byte count.

PDF type	Usual cause	What to try first
Exported slides	Full-size image per slide	Re-export from Keynote at screen quality
Scans	High DPI on every page	Re-scan at 150 to 200 DPI, or compress in Preview
Photo inserts	Large JPEG embedded in the doc	Export with Reduce File Size, then check charts
Mixed reports	Charts plus hi-res logos	Re-export from source app when you still have it

If you built the PDF from JPEG scans, see JPG to PDF on Mac for the merge step, then come back here to shrink the result.

Shrink one PDF in Preview

Preview ships with every Mac and handles a single PDF without extra installs:

1. Open the PDF in Preview.
2. Choose File → Export…
3. Set Quartz Filter → Reduce File Size
4. Save as a new file (keep the original until you check quality).

Zoom in on charts, small type, and signature lines. If text looks muddy, undo and re-export from Keynote instead of filtering harder. Preview is a one-file tool: fine for a contract or invoice, slow when you have a folder of decks from last quarter.

For image-heavy scans where Preview over-softens detail, open Terminal (Applications → Utilities → Terminal), install Ghostscript through Homebrew if you need finer control:

brew install ghostscript
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook \
  -dNOPAUSE -dQUIET -dBATCH -sOutputFile=compressed.pdf input.pdf

The /ebook profile is a reasonable starting point for screen reading. Adjust only after you compare a sample page side by side with the original.

Re-export from Keynote or PowerPoint

If you still have the deck, exporting the PDF again often beats crushing an already huge file:

1. Open the source in Keynote or PowerPoint.
2. Export PDF at lower image quality or a slide size meant for screen viewing, not print.
3. Compare one chart-heavy slide before you send the full deck.

Slide apps embed each slide as a bitmap. Exporting at 1280 px or 1920 px wide is usually enough for laptops and projectors. Print-quality exports belong in a separate file you archive, not in the version you email.

When a PDF came from a scan pipeline rather than slides, split pages to images only if you need per-page edits. Otherwise keep the PDF intact and compress it as one document. See PDF to images on Mac when reviewers want PNG or JPEG pages instead.

For decks you receive as PDF only, ask for the source KEY or PPTX when quality matters. Re-export beats repeated Quartz filters when small type already looks soft after the first pass.

Common email and portal limits

Upload forms and mail servers rarely tell you why a PDF failed. The limit is almost always total attachment size, not page count.

Destination	Typical limit	Practical starting point
Corporate email	10 to 25 MB per message	Aim under 8 MB for headroom
Web forms and portals	5 to 20 MB per file	Compress before upload, keep a master copy
Shared drives	Higher caps, slow on mobile	Still worth shrinking for reviewers on phones
Print shops	Often no strict cap	Use the uncompressed master for print

When a PDF sits just above the limit, re-export from the source app once before you run aggressive filters. A second pass of heavy compression can blur text that was already borderline.

If you merge many JPEG scans into one PDF, the combined file can exceed limits even when each photo looked small on its own. Compress after merge, not only before.

Test the final file on the same network your recipients use. A PDF that uploads fine on office Wi-Fi can still fail on a phone hotspot when the portal timeout is short.

Using GetCompress

GetCompress processes PDF files locally on your Mac. Nothing uploads to a server, which matters for contracts, HR packets, and unreleased decks.

• Drag one PDF or a folder of decks and scans into GetCompress.
• Pick a PDF compression preset (GetCompress optimizes embedded images inside the file; no need to pick a megabyte target by hand).
• Preview pages when charts, maps, or small type matter before you export.
• Batch a whole folder when quarterly reports or scan batches share the same preset.
• Save the preset you used so the next compress PDF on Mac pass takes one click.

GetCompress does not replace Preview for a quick single-file filter, and it does not edit slide layout. It shines when you repeat the same optimization on many PDF files without opening each one separately. For a broader cleanup pass across PDF, video, and images, see reduce file size on Mac .