Mac has built-in PDF tools — Preview and ColorSync Utility — but their compression results are often disappointing, and sometimes they make files larger. This guide covers all four methods for compressing PDFs on Mac, why the built-in options frequently fail, and the most reliable free alternative.
The most predictable way to compress a PDF on Mac is a browser-based tool. Works in Safari, Chrome, or Firefox — no app download, no account required.
1
Open ShrinkPDF in Safari or Chrome
Go to ShrinkPDF.fyi. Works on macOS Monterey, Ventura, Sonoma, and Sequoia.
2
Drag Your PDF from Finder
Open Finder, locate your PDF, and drag it directly onto the ShrinkPDF page. Or click "Choose PDF File" and browse. No file size limit.
3
Select Compression Level and Compress
Choose Maximum for portal or submission uploads. Choose Balanced for email or general sharing. Processing happens in your browser — your file never leaves your Mac.
4
Download — File Saves to Downloads
Click Download. Safari saves the file to your Downloads folder. Open it to verify size and quality before submitting.
Method 2: Preview — Export as PDF (Reduce File Size)
macOS Preview has a built-in "Reduce File Size" quartz filter. It's convenient — no extra software needed — but results are highly inconsistent.
1
Open the PDF in Preview
Double-click the PDF to open it in Preview (the default PDF viewer on Mac). Or right-click → Open With → Preview.
2
File → Export as PDF
Click File in the menu bar → Export as PDF (not "Export" or "Print").
3
Click the Quartz Filter Dropdown
In the Export dialog, click the Quartz Filter dropdown at the bottom. Select Reduce File Size. Choose a save location and click Save.
4
Check the Result
Compare the new file size to the original. Right-click the file → Get Info. If the file is larger than the original, the quartz filter made it worse — use Method 1 instead.
Method 3: ColorSync Utility
ColorSync Utility is a macOS tool primarily for colour management, but it can also apply PDF filters including compression. It gives slightly more control than Preview.
1
Open ColorSync Utility
Press Command + Space, type "ColorSync Utility", and press Enter. Or find it in Applications → Utilities.
2
Open Your PDF
In ColorSync Utility, go to File → Open and select your PDF. The document will appear in the viewer panel.
3
Apply the Reduce File Size Filter
At the bottom of the window, find the Filter dropdown. Select Reduce File Size. Click the triangle/arrow button to apply and save. Choose a filename and location.
Results from ColorSync are similar to Preview — workable for some files, but the quartz filter used is the same underlying engine, so PDFs with unusual encoding may still get larger.
Method 4: Automator (Batch Compression)
If you need to compress many PDFs at once on Mac, Automator can batch-process them with the same Reduce File Size filter. Useful for recurring workflows.
1
Open Automator
Go to Applications → Automator, or search with Spotlight. Choose "New Document" → Workflow.
2
Add the PDF Filter Action
In the search bar, type "PDF". Find Apply Quartz Filter to PDF Documents and drag it into the workflow area.
3
Set to Reduce File Size
In the action, set the Filter to Reduce File Size. Add a "Copy Finder Items" action before it to save compressed copies to a specific folder.
4
Run on Your PDFs
Drag your PDFs onto the Automator workflow or run it via File → Run. The compressed copies will appear in your designated folder.
Why Preview Often Fails or Makes Files Larger
This is one of the most common frustrations Mac users encounter. You apply "Reduce File Size" in Preview and the resulting PDF is the same size — or larger. Here's why:
The quartz filter uses a fixed low-resolution target — it downsamples all images to 72 DPI. If the images in your PDF are already at 72–96 DPI (common in web-created PDFs), there's nothing to reduce and the file may actually grow due to re-encoding overhead.
It doesn't handle all PDF content types well — PDFs with mixed content (vector + raster), PDFs created by design software, or PDFs with unusual encoding often respond poorly to the quartz filter.
No compression level control — unlike dedicated tools, Preview gives you one option (Reduce File Size) with no way to adjust aggressiveness.
When Preview compression works vs fails
Works well: Scanned PDFs at 300 DPI colour, large photos embedded in PDFs, PDFs created by cameras or scanners
Fails or makes larger: PDFs created from Word/Pages, web-optimised PDFs, PDFs with vector graphics, PDFs already at low resolution
If Preview's result is not smaller than the original, use Method 1 (ShrinkPDF) — it applies smarter, content-aware compression that works regardless of how the PDF was created.
Method Comparison
Which Method to Use on Mac
Most reliable, any PDF: Method 1 (ShrinkPDF in browser) — predictable 65–85% reduction
No internet, try built-in first: Method 2 (Preview) — free, convenient, but inconsistent results
Batch compress many files: Method 4 (Automator) — good for workflows, same quartz filter limitations
Need to install nothing: Method 1 in Safari — zero install required
✓ Try ShrinkPDF Free — No Login Required
No registration. No file size limit. Your file never leaves your browser.
Why did Preview make my PDF larger instead of smaller? ▼
Preview's Reduce File Size filter downsamples images to 72 DPI. If your PDF's images are already at low resolution, there's nothing to reduce — the re-encoding process can actually add overhead. This is a known limitation. Use ShrinkPDF instead for consistent results.
Can I compress a PDF on Mac without downloading any app? ▼
Yes. ShrinkPDF runs in Safari, Chrome, or Firefox — no app download required. Open shrinkpdf.fyi, upload your PDF, compress, and download. Alternatively, macOS Preview is pre-installed and can reduce some PDF file sizes using the Quartz Filter.
Does compressing a PDF on Mac affect its quality? ▼
Text is never affected — it remains perfectly sharp regardless of compression. Images are reduced in resolution — at Maximum compression, images go from 300 DPI to approximately 150 DPI, which is still clear for on-screen reading. Always open the compressed file to verify before submitting.
How do I compress a PDF on Mac for email? ▼
Use ShrinkPDF with Balanced compression — open shrinkpdf.fyi in Safari, upload the PDF, select Balanced, and download. Balanced compression reduces most PDFs by 40–60% with virtually no visible quality change, making it ideal for email attachments.
Will Preview's compression work on scanned PDFs? ▼
Yes — scanned PDFs at 300 DPI colour are one of the cases where Preview's Reduce File Size filter works reasonably well, because there's actual resolution to reduce. However, ShrinkPDF typically achieves better reduction (70–85% vs 50–70%) on the same scanned files.