Most email providers limit attachment sizes to 10–25 MB. Scanned documents, design files, and reports easily exceed this. A 30 MB scanned PDF that Gmail refuses to send is a common, fixable problem.
This guide covers every way to compress a PDF on a Mac before emailing it — without uploading your document to an external service.
Why PDFs Get Large
PDF file size depends on what is inside:
- Scanned documents — each page is a high-resolution image. A 300 DPI colour scan of a 10-page document can easily be 20–50 MB.
- Embedded images — high-resolution images embedded in a designed PDF add significant size.
- Fonts — PDFs embed font data, which adds a few MB for complex documents.
- Unoptimised exports — PDFs exported from apps like InDesign, Word, or Keynote at default settings are often larger than necessary.
Method 1: macOS Preview — Reduce File Size
Preview's built-in PDF compression is the fastest option:
- Open your PDF in Preview.
- Go to File → Export as PDF…
- In the dialog, click the Quartz Filter dropdown at the bottom.
- Choose Reduce File Size.
- Name the file, choose a location, and click Save.
What to expect: Preview's Reduce File Size filter can dramatically reduce file size — but it sometimes over-compresses images and produces blurry text in scanned documents. Test the result before sending.
To get better results with Preview, you can create a custom Quartz filter with higher image quality settings via ColorSync Utility, but that requires several extra steps.
Method 2: PDFZero — Three Compression Levels
PDFZero offers three compression levels so you can balance file size against quality:
- Open PDFZero.
- Drag your PDF into the app or click to open it.
- Click Compress.
- Choose a compression level:
- Low — gentle compression, highest quality retained. Best for documents with important images or text.
- Medium — balanced quality and size reduction. The default for most use cases.
- High — maximum compression. Good for scanned documents where exact image quality is less important.
- PDFZero shows the original file size before you export. Click Export to save the compressed version.
Everything happens locally on your Mac — your PDF is never uploaded anywhere.
PDFZero is free to use with 2 uses per session (single-page PDFs up to 20 pages). A license removes all limits.
Method 3: Automator (Batch Compression)
If you regularly need to compress PDFs, Automator can build a workflow that applies to any PDF you drop on it:
- Open Automator and create a Quick Action.
- Set it to receive PDF files in Finder.
- Add the PDF: Apply Quartz Filter to PDF Documents action.
- Set the Quartz filter to Reduce File Size.
- Save the Quick Action.
Your workflow appears in the right-click menu for any PDF file. This is free but uses Preview's Reduce File Size algorithm, with the same quality trade-offs.
How Much Can You Reduce a PDF?
Results vary by content:
| PDF type | Typical reduction |
|---|---|
| Scanned document (300 DPI colour) | 60–85% smaller |
| Scanned document (300 DPI black and white) | 30–60% smaller |
| Designed PDF with images | 20–50% smaller |
| Text-only PDF | 5–20% smaller |
A scanned 30 MB document at high compression often comes down to 3–6 MB — easily under any email attachment limit.
What If the PDF Is Still Too Large?
If compression alone doesn't bring the file under the email size limit:
- Split the PDF — PDFZero can split a PDF by page range. Send each section in a separate email.
- Use a file transfer service — WeTransfer, Google Drive, Dropbox, or iCloud Drive can send large files by sharing a link instead of an attachment.
- Reduce scan resolution — if you are scanning the document yourself, scan at 150 DPI instead of 300 DPI for a significant size reduction without visible quality loss in most documents.
Preserving Quality for Documents With Important Images
If your PDF contains charts, photos, or high-resolution diagrams that matter, use PDFZero's Low compression level — it reduces file size without visibly degrading images. Always open the compressed PDF and check it looks acceptable before emailing.
FAQ
Will compressing the PDF make text blurry? Text in properly structured PDFs (not scanned) is stored as vector data, not as pixels — it stays sharp at any compression level. Scanned PDFs store pages as images; high compression can blur scanned text. Use Medium or Low compression for scanned documents with important text.
Can I compress password-protected PDFs? You generally need to remove the password before compressing. Preview and PDFZero can compress password-protected PDFs if you provide the password to open the file, but some DRM-protected PDFs block modification entirely.
Is there a free way to compress PDFs on Mac? Yes — macOS Preview is free and built in. PDFZero offers 2 free compressions per session.
Does compressing a PDF change the number of pages? No. Compression reduces image quality and removes redundant data, but the page count stays the same.
Summary
For occasional one-off compression, macOS Preview's Reduce File Size option is fast and free. For better control over quality — or for documents where visual quality matters — PDFZero's three compression levels let you choose the right balance before exporting. Your PDF is never uploaded.
Browse more guides in the PDF category or read how to merge multiple PDFs on Mac.