How to Reduce PDF File Size on a Mac

The fastest way to shrink a PDF on your Mac

The simplest method is to use the Preview app that comes built into every Mac. Open your PDF in Preview, go to File > Export, and in the Quartz Filter dropdown choose "Reduce File Size". This single step compresses images inside the PDF and usually cuts the file down by 30 to 50 percent without making text unreadable. The trade-off is that photos and graphics will look slightly softer, but for documents you plan to email or store, the size savings are worth it.

If that one-step method does not shrink the file enough, or if you need more control over what gets compressed, the other methods below let you choose how aggressively to compress and what parts of the PDF to target.

Key Takeaways

Preview's "Reduce File Size" filter is the fastest method and works for most PDFs without requiring any other software.
If you need stronger compression, you can export as PDF again and choose different Quartz Filters or adjust image resolution manually.
Compressing a PDF in Preview does not change the original file — you must export or save as a new file to keep the smaller version.
For PDFs with many high-resolution photos, compression usually shrinks the file by 40 to 60 percent, but text-heavy PDFs may shrink less.

Using Preview's export settings for more control

If the standard "Reduce File Size" filter does not compress enough, Preview lets you adjust image quality and resolution during export. Open the PDF in Preview, then go to File > Export. In the dialog that opens, click the blue "Options" button to reveal additional settings.

You will see a dropdown for "Quartz Filter" — this is where you choose the compression method. "Reduce File Size" is the default, but you can also try "Lightness Decrease" or "Remove Black Borders" if those explore to your document. Below that, you can manually set the image resolution (measured in DPI, or dots per inch). Lowering this from 300 DPI to 150 DPI cuts image file size roughly in half. For documents meant to be read on screen or printed at normal size, 150 DPI is usually fine. For documents that will be printed large or need photo quality, stick with 200 DPI or higher.

After you adjust these settings, click Save. Preview will create a new compressed PDF file and leave your original untouched.

Compressing PDFs created from scans or photos

PDFs made from scanning paper documents or photographing pages tend to be much larger than PDFs created from word processors, because they contain full-resolution images. These compress especially well. Open the PDF in Preview, go to File > Export, and choose "Reduce File Size" from the Quartz Filter dropdown. Scanned PDFs often shrink by 60 to 80 percent this way because Preview can aggressively compress the image data without affecting readability of text.

If the result is still too large, try exporting again and manually lowering the DPI to 150 or even 100. At 100 DPI, a scanned document remains readable on screen and prints clearly at normal size, but the file becomes much smaller. Test by opening the compressed version and zooming in on text — if it stays sharp, the compression worked.

When to use third-party tools instead of Preview

Preview handles most PDFs well, but some situations call for other software. If your PDF contains forms that users need to fill in, compression sometimes makes form fields harder to click or read. If your PDF has interactive elements like buttons or links, Preview's compression may affect them. In these cases, dedicated PDF software like PDFtk or Coherence X gives you finer control over what gets compressed and what stays untouched.

You can also use online PDF compressors, but be cautious: uploading a PDF to a website means the file passes through someone else's server. If your PDF contains sensitive information, use Preview or desktop software instead. For everyday documents, Preview is faster and keeps everything on your Mac.

Checking file size before and after compression

To see how much space you actually saved, find the PDF in Finder, right-click it, and choose "Get Info". The window that opens shows the file size in both bytes and megabytes. Write down the original size, then compress the PDF and check the size again. This tells you whether the compression was worth the effort — if you only saved a few percent, the file may not have been compressible to begin with.

PDFs that compress well are usually those with embedded images or photos. PDFs that are mostly text, or PDFs that have already been compressed once, may not shrink much further. If you compress a PDF multiple times, each pass produces smaller gains, so there is a point where further compression is not worth your time.

Saving your compressed PDF in the right place

When you export a compressed PDF from Preview, give it a new name so you do not accidentally overwrite the original. A straightforward naming method is to add "-compressed" to the end of the filename: "report.pdf" becomes "report-compressed.pdf". This way, if the compressed version does not work for your purpose, you still have the original.

Store the compressed version in the same folder as the original, or move it to a cloud storage folder like iCloud Drive or Dropbox if you plan to share it. If you are compressing PDFs regularly — for example, before emailing them — consider creating a dedicated folder for compressed files so they do not clutter your Documents folder.

Frequently Asked Questions

Will compressing a PDF make the text blurry or hard to read?

Text usually stays sharp because Preview compresses images and graphics more aggressively than text. If you use the standard "Reduce File Size" filter, text remains readable. If you manually lower the DPI below 150, text may soften slightly on screen, but it prints clearly at normal size.

Can I compress a PDF that is already password-protected?

Yes, you can open and export a password-protected PDF in Preview without removing the password. The compressed version will keep the same password protection. If you want to remove the password, you will need different software, as Preview does not have that feature.

What is the smallest file size I can get a PDF down to?

That depends entirely on what is in the PDF. A text-heavy document may only shrink 10 to 20 percent. A PDF full of high-resolution photos can shrink 60 to 80 percent. There is no universal minimum — compression stops being effective once the file has been reduced as much as the content allows.

Do I need to install anything to use Preview's compression?

No. Preview comes built into every Mac and the Quartz Filters it uses are part of macOS. You do not need to read or install any software to compress a PDF using Preview.

Can I compress multiple PDFs at once?

Preview does not have a batch compression feature, so you must compress PDFs one at a time. If you regularly compress many files, you might look into Automator (built into Mac) or third-party tools that can process multiple PDFs in one action, though Preview is usually fast enough for occasional use.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.