The fastest way to compress a PDF on Mac
The built-in Preview app on your Mac can compress a PDF in about 30 seconds without installing anything. Open the PDF in Preview, go to File > Export, choose PDF from the format dropdown, then click the Quartz Filter dropdown and select "Reduce File Size". This shrinks the file by lowering image resolution and removing some metadata, but the PDF stays readable and printable.
If you need more control over what gets compressed, Mac's native tools give you options. You can also use the command line if you're comfortable with that, or drag files into third-party apps designed specifically for compression. The method you pick depends on how much smaller the file needs to be and whether you care about keeping high-quality images inside it.
Key Takeaways
- Preview's "Reduce File Size" filter compresses most PDFs by 30 to 50 percent and works without any extra software.
- Quartz filters in Preview let you choose between "Reduce File Size", "Lighter" (more compression), and "Lighter 2" (maximum compression) depending on your needs.
- The command line tool gs (Ghostscript) gives you precise control over image quality and file size if you're willing to type commands.
- Third-party apps like Compressor or PDF Squeezer add a drag-and-drop interface but cost money and aren't necessary for most compression tasks.
- Compressed PDFs lose image quality permanently — test on a copy first if the document contains photos or detailed graphics you need to preserve.
Using Preview's built-in compression
Preview is the simplest route because it's already on your Mac. Open the PDF you want to compress, then click File in the menu bar. Select Export (not Save As — Export is what lets you change the format and compression settings). A dialog box opens.
In the dialog, make sure the Format dropdown shows "PDF". Below that, you'll see a Quartz Filter dropdown that defaults to "None". Click it and choose one of three options: "Reduce File Size" (standard compression), "Lighter" (more aggressive), or "Lighter 2" (maximum compression). Pick the one that matches how much smaller you need the file to be. Then click Save and choose where to put the compressed version.
The trade-off is that all three filters reduce image quality. "Reduce File Size" usually shrinks the file by 30 to 50 percent and keeps images reasonably clear. "Lighter" and "Lighter 2" compress more aggressively but make photos and graphics look noticeably softer. Always test on a copy of the original file first, especially if the PDF contains images you need to read clearly.
Using the command line for precise control
If you want to set exact image quality levels, the command line tool gs (Ghostscript) gives you that power. You'll need to install Ghostscript first — the easiest way is through Homebrew, a package manager for Mac. If you don't have Homebrew, open Terminal (in Applications > Utilities) and paste this command, then press Enter:
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
Once Homebrew is installed, paste this command to install Ghostscript:
brew install ghostscript
Now you can compress a PDF by typing a command like this (replace input.pdf and output.pdf with your actual filenames):
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -r150x150 -o output.pdf input.pdf
The -dPDFSETTINGS option controls compression: use /screen for maximum compression (lowest quality), /ebook for medium compression, or /printer for minimal compression (highest quality). The -r150x150 sets image resolution to 150 DPI — lower numbers compress more but reduce clarity. This method takes longer to set up but gives you exact control over the trade-off between file size and quality.
When to use third-party apps
Apps like PDF Squeezer, Compressor, or PDFtk Pro add a graphical interface and sometimes batch processing (compressing multiple files at once). They cost between $10 and $30 and aren't necessary if you only compress PDFs occasionally. But if you compress dozens of files regularly, the drag-and-drop interface saves time compared to opening Preview for each one.
Some third-party apps also let you compress by removing elements — like stripping out embedded fonts or deleting images entirely — rather than just lowering quality. That's useful if your PDF contains things you don't need. Before buying, check whether the app's compression method matches what you're trying to do. Many of them use Ghostscript under the hood anyway, so you're often paying for convenience rather than a fundamentally different result.
What happens to your PDF when it compresses
Compression works by reducing image resolution, removing color information, and stripping out metadata like creation date and author name. A PDF with photographs shrinks more than a text-only PDF because images take up the most space. Lowering resolution from 300 DPI (print quality) to 150 DPI (screen quality) cuts file size significantly but makes photos look softer on screen and print less sharply.
Text inside a PDF usually stays crisp because it's stored as outlines rather than images. But if the PDF contains scanned documents (which are really just images of pages), compression makes the text fuzzier. Always open the compressed version and check a few pages before you delete the original. If the quality isn't acceptable, you can't undo compression — you'll need to start over with the uncompressed file.
Comparing compression methods side by side
| Method | Setup time | Compression amount | Quality control | Cost |
|---|---|---|---|---|
| Preview (Reduce File Size) | 30 seconds | 30–50% | Low (preset only) | Free |
| Preview (Lighter) | 30 seconds | 50–70% | Low (preset only) | Free |
| Ghostscript command line | 10 minutes (first time) | 30–80% | High (adjustable settings) | Free |
| Third-party app (PDF Squeezer, etc.) | 2 minutes | 30–70% | Medium (app-dependent) | $10–$30 |
Frequently Asked Questions
Can I compress a PDF without losing image quality?
Not significantly. Compression always reduces quality to some degree — that's how it shrinks file size. You can minimize the loss by using Preview's "Reduce File Size" filter instead of "Lighter", or by setting Ghostscript to /printer quality. But if your PDF contains high-resolution photos, expect them to look softer after compression.
Why is my compressed PDF still large?
PDFs with many high-resolution images compress less than text-heavy PDFs. If the file barely shrinks, the PDF may contain embedded fonts, videos, or other elements that compression doesn't touch. Try the "Lighter" or "Lighter 2" filter in Preview for more aggressive compression, or use Ghostscript with /screen quality to compress as much as possible.
Can I compress a PDF that's password-protected?
Preview can usually open and export password-protected PDFs if you know the password. Enter the password when prompted, then use Export as normal. Some third-party apps may have trouble with protected PDFs — test on a copy first.
What's the difference between exporting and saving in Preview?
Save As keeps the PDF in its original format with no compression. Export lets you choose a format (PDF, image, etc.) and explore filters like compression. Always use Export when you want to compress.
Should I keep the original PDF after compressing?
Yes, at least until you've checked the compressed version and confirmed the quality is acceptable. Compression is permanent — you can't restore lost image detail from a compressed file. Keep the original as a backup if the document matters.