Learning how to compress a PDF on Mac can help when a document is too large to email, upload to a website, submit for an assignment, or share with colleagues. PDF files containing high-resolution images, scanned pages, graphics, and embedded fonts can quickly become larger than expected.
Fortunately, macOS offers several ways to reduce PDF file size. You can use the built-in Preview app, an online PDF compressor, Adobe Acrobat, or optimize the original document before exporting it as a PDF.
The best method depends on your document, the software available on your Mac, and how much image quality you want to preserve.
In this guide, you'll learn five easy methods to compress PDF files on Mac, including free options, how to reduce file size without unnecessary quality loss, and what to do when a PDF remains too large.
Quick Answer: How to Compress a PDF on Mac
You can compress a PDF on Mac using the built-in Preview application:
Open your PDF in Preview.
Click File → Export.
Open the Quartz Filter dropdown.
Select Reduce File Size.
Choose a location and save the compressed PDF.
Compare the new file size and quality with the original.
Alternatively, you can use the OneFileKit PDF Compressor to reduce PDF file size directly through Safari, Chrome, or another browser.
Tip: Preview's Reduce File Size filter can noticeably reduce image quality. Always check the compressed document before sharing it.
Method 1: Compress a PDF on Mac Using Preview
Preview is a built-in macOS application that allows you to open, view, annotate, and perform basic operations on PDF files.
One of its useful features is the ability to export PDFs using a file-size reduction filter.
Step 1: Open Your PDF in Preview
Locate the PDF in Finder.
Double-click the file if Preview is your default PDF viewer, or right-click and choose Open With → Preview.
Step 2: Select File → Export
From the top menu bar, click File, then select Export.
Make sure you choose Export rather than simply saving the existing document.
Step 3: Choose Reduce File Size
In the export window, locate the Quartz Filter dropdown.
Select Reduce File Size.
This tells Preview to apply its built-in PDF optimization filter.
Step 4: Save the Compressed PDF
Choose a filename and destination.
Click Save.
To protect your original file, save the compressed version under a different filename.
Step 5: Compare File Size and Quality
Open Finder and select both PDF files.
Use Get Info to compare their sizes.
Then open the compressed PDF and check its text, images, diagrams, and page layout.
Advantages of Preview
Built into macOS
No additional software required
Works offline
Simple export process
Suitable for occasional PDF compression
Limitations of Preview
Preview doesn't offer the same detailed compression controls as specialized PDF optimization software.
Its Reduce File Size filter can also noticeably affect image sharpness, particularly in image-heavy PDFs.
For more information, see Apple's official guide to reducing PDF size in Preview.
Method 2: Compress a PDF on Mac Online With OneFileKit
If you want to control the balance between PDF size and visual quality, an online PDF compressor is another practical option.
The OneFileKit Compress PDF tool works through a browser, so you don't need to install a separate application.
Step 1: Open OneFileKit
Launch Safari, Google Chrome, Firefox, or another modern browser on your Mac.
Visit:→https://onefilekit.com/compress-pdf
Step 2: Upload Your PDF
Click Choose PDF File, or drag and drop your document into the upload area.
OneFileKit currently supports PDF uploads up to 100 MB.
Step 3: Choose Your Compression Level
OneFileKit offers three compression options.
Basic Compression
Prioritizes higher visual quality while attempting to reduce file size. Suitable for documents containing images and graphics.
Strong Compression
Balances file-size reduction with practical visual quality. Useful for everyday document sharing.
Maximum Compression
Prioritizes the smallest practical PDF size, potentially applying stronger image compression.
Step 4: Start Compression
Click Compress PDF.
The tool processes your document using the selected compression level.
Processing time depends on the file's size and complexity.
Step 5: Download the Smaller PDF
When compression finishes, download the resulting file.
Check whether it meets your upload or sharing requirements.
If the PDF remains too large, try a stronger compression level and review the resulting quality.
Why Use OneFileKit on Mac?
Works through Safari, Chrome, and other browsers.
No separate desktop installation.
Three compression levels.
Supports PDFs up to 100 MB.
Suitable for documents, reports, assignments, and presentations.
Provides a straightforward upload, compress, and download workflow.
Note: Compression results vary depending on the original document. A smaller output size is not guaranteed for every PDF.
Method 3: Reduce PDF File Size on Mac With Adobe Acrobat
Adobe Acrobat provides additional PDF optimization features, making it useful for people who regularly work with complex documents.
Some advanced optimization features may require a paid Acrobat subscription.
Step 1: Open Adobe Acrobat
Launch Adobe Acrobat on your Mac.
Open the PDF you want to compress.
Step 2: Find the PDF Compression Tool
Depending on your Acrobat version, select the option for compressing or optimizing a PDF.
Step 3: Choose Optimization Settings
Where supported, Adobe Acrobat can provide controls for:
Image compression
Image resolution
Font resources
Document objects
Other PDF optimization settings
Step 4: Save the Optimized PDF
Save the output as a separate document.
Compare its file size and appearance with the original.
When Should You Use Adobe Acrobat?
Adobe Acrobat may be appropriate when you need more advanced controls, work with PDFs professionally, or already have an Acrobat subscription.
For detailed instructions, consult Adobe's official PDF file-size reduction guide.
Method 4: Compress a PDF on Mac by Optimizing the Original Document
Sometimes the best way to reduce PDF file size is to return to the original document.
For example, you may have created your PDF using:
Microsoft Word
Apple Pages
Microsoft PowerPoint
Keynote
A design application
A scanning application
If the original file is available, you may be able to produce a smaller PDF by adjusting its contents and export settings.
Step 1: Open the Original Document
Open the source file in the application where it was created.
Step 2: Optimize Large Images
Review the images used in the document.
High-resolution images can significantly increase PDF file size.
Where appropriate, resize or compress images before exporting.
Step 3: Check Export Settings
Look for PDF export settings that prioritize smaller file size or online viewing.
Different applications offer different options.
Step 4: Export a New PDF
Create a new PDF using the optimized settings.
Compare it with the original export.
Why This Method Can Work
Reducing unnecessary data before PDF creation can sometimes produce a smaller document without requiring aggressive compression afterward.
This approach is particularly useful for presentations, portfolios, brochures, and image-heavy reports.
Method 5: Compress Scanned PDFs on Mac
Scanned PDFs can be especially large because they often contain full-page images rather than ordinary digital text.
A document scanned at a high resolution may consume substantially more storage than necessary for ordinary screen viewing.
Step 1: Check Whether the PDF Is Scanned
Open the PDF in Preview.
Try selecting individual words.
If the page behaves like a single image, the PDF may be image-based.
Step 2: Consider the Intended Use
If you only need the PDF for screen viewing or an online submission, very high-resolution scans may be unnecessary.
However, documents containing small text, signatures, or detailed diagrams need sufficient resolution to remain readable.
Step 3: Compress the Scanned PDF
Use Preview, Adobe Acrobat, or an online PDF compressor.
Start with a quality-preserving option.
Step 4: Review the Result
Pay special attention to:
Small printed text
Signatures
Stamps
Tables
Handwritten notes
Fine lines
Document edges
Does OCR Reduce PDF File Size?
OCR, or Optical Character Recognition, identifies text within scanned images.
OCR does not automatically guarantee a smaller PDF. In some workflows, adding a searchable text layer can even increase file size.
If your goal is searchable or editable text, explore the OneFileKit PDF OCR tool.
How to Reduce PDF File Size on Mac Without Losing Quality
One of the most common concerns is whether PDF compression will damage the document's appearance.
The answer depends on the compression method and the content of the PDF.
Some optimizations can reduce file size without visible changes, while others reduce image resolution or quality.
Use the Lightest Effective Compression
Start with Basic compression.
If the resulting PDF meets your size requirement, stronger compression may be unnecessary.
Keep the Original PDF
Always retain an original copy of important documents.
Check Image Quality
Review photographs, charts, screenshots, and illustrations after compression.
Avoid Repeated Lossy Compression
Repeatedly compressing an already compressed PDF may produce diminishing size reductions while reducing image quality.
Compare the Results
Open both PDFs side by side and inspect the sections where image quality matters most.
Preview vs OneFileKit vs Adobe Acrobat: Which Is Better?
Feature | Preview | OneFileKit | Adobe Acrobat |
|---|---|---|---|
Works on Mac | Yes | Yes | Yes |
Browser-based | No | Yes | Optional |
Requires installation | Built into macOS | No | Desktop version does |
Compression controls | Basic filter | 3 levels | Advanced options |
Works offline | Yes | No | Desktop version can |
Best for | Quick local compression | Easy browser compression | Detailed PDF optimization |
Why Is My PDF File So Large on Mac?
PDF file size depends on the resources contained within the document.
Common causes include:
High-resolution images: Large photographs and graphics can increase file size.
Scanned pages: A scanned PDF may store each page as an image.
Embedded fonts: Some documents include font data.
Complex graphics: Detailed illustrations and vector graphics can add data.
Multiple pages: Long documents may require more storage.
Existing export settings: High-quality export settings can produce larger files.
Understanding the source of the file size helps you choose an appropriate compression method.
How Much Can You Reduce PDF Size on Mac?
There is no fixed compression percentage.
For example, an image-heavy PDF may shrink significantly, while a small text-based PDF that has already been optimized may barely change.
The result depends on the document's contents, original compression, and selected settings.
A trustworthy compressor should prioritize a useful balance between file size and document quality rather than promise the same reduction for every file.
How to Compress a PDF on Mac for Email
If a PDF is too large to attach to an email, follow these steps:
Check the email provider's attachment-size limit.
Open the PDF in Preview or OneFileKit.
Apply a suitable compression level.
Save or download the smaller PDF.
Check its readability and size.
Attach it to your email.
If the file remains too large, consider using a cloud-storage sharing link instead.
How to Compress a PDF on Mac for University or Job Applications
Universities, recruitment platforms, and government websites may impose file-size limits on document uploads.
You may need to compress:
CVs and resumes
Academic transcripts
Certificates
Portfolios
Assignment files
Application forms
Supporting documents
Before uploading, check the exact maximum size permitted.
Choose a compression level that meets the requirement while keeping all important information readable.
For sensitive documents, consider the privacy and retention policies of any online tool before uploading.
Why Is My PDF Still Large After Compression?
Sometimes a PDF remains large even after compression.
This may happen because:
The original file is already optimized.
Images are already compressed.
The PDF contains many pages.
The compression settings prioritize quality.
Some document resources cannot be reduced substantially.
Try a stronger compression setting if appropriate.
If you still have the original source document, optimizing it before exporting may provide another option.
Is It Safe to Compress a PDF Online on Mac?
Online PDF compression requires sending your document to a service for processing.
Before uploading sensitive files, review the provider's privacy and file-retention practices.
OneFileKit's Compress PDF page states that uploaded and processed files are automatically cleaned up after 60 minutes. This should be verified against the production storage configuration.
For confidential financial, legal, or personal documents, a suitable offline solution may be preferable.
Final Thoughts
Knowing how to compress a PDF on Mac gives you several practical ways to reduce document size without recreating the entire file.
For occasional compression, Preview is a convenient built-in solution.
If you want a browser-based compressor with different quality settings, use the OneFileKit PDF Compressor.
For professional document workflows requiring detailed optimization controls, Adobe Acrobat may be more suitable.
Whichever method you choose, start with the lightest effective compression and compare the output with the original document before sharing it.
