The fastest way to reduce a PDF on Mac is through Preview, the built-in app that comes with every Mac

Open the PDF in Preview (double-click it, or right-click and choose Open With > Preview). Go to File > Export As. Before you click Export, look for the Quartz Filter dropdown menu — it defaults to "None". Click that dropdown and select Reduce File Size. Then click Export, choose where to save it, and you're done. The compressed version will be noticeably smaller, usually 30 to 50 percent of the original size, depending on what's in the PDF.

This works because PDFs often contain extra data — multiple versions of images, embedded fonts, metadata — that you don't need. The Reduce File Size filter strips those out. The trade-off is that image quality drops slightly, but for most uses (email, sharing documents, uploading to forms), the loss is invisible.

Key Takeaways

  • Preview's Reduce File Size filter is built into every Mac and requires no read or setup.
  • The compressed file is typically 30 to 50 percent smaller, with image quality loss that is usually unnoticeable for documents and forms.
  • You can also compress during export by adjusting image quality manually if you want more control over the final size.
  • For PDFs with many high-resolution images, web-based tools or dedicated Mac apps offer additional compression options if Preview's filter is not enough.

Using Preview's manual compression settings for more control

If the automatic Reduce File Size filter makes the PDF too blurry or you want to fine-tune the compression, Preview lets you adjust image quality yourself. Open the PDF in Preview, go to File > Export As, and look for the Quartz Filter dropdown again. This time, select Reduce File Size and then click the Options button that appears below it.

A panel opens with sliders for image quality and resolution. Lower the image quality slider to compress more aggressively, or lower the resolution (measured in DPI, or dots per inch) if the PDF contains scans or photos. Start with small changes — move the quality slider down by 10 to 20 percent and export a test copy. If it still looks good, you can go lower next time. This approach takes a few extra minutes but gives you control over the balance between file size and readability.

When to use other tools instead of Preview

Preview works well for most PDFs, but some situations call for a different approach. If your PDF is mostly text with very few images, Preview's compression may not shrink it much — text-heavy PDFs are already fairly small. If your PDF contains scanned documents and you need the smallest possible file, dedicated compression tools often do better because they can re-encode images more efficiently.

Mac App Store apps like PDF Squeezer or PDF Compressor offer batch processing (compress multiple PDFs at once) and sometimes achieve smaller file sizes than Preview. Web-based tools like ilovepdf.com or smallpdf.com also work on Mac — you upload the PDF, they compress it, and you read the result. The downside is that your file leaves your computer, which matters if the PDF contains sensitive information. For private documents, Preview is safer.

Understanding what makes a PDF large

PDFs get bloated for a few reasons. High-resolution images embedded in the file take up the most space — a single photo at 300 DPI (print quality) can be several megabytes. Fonts are another culprit; if the PDF embeds every font used, that adds weight. Metadata (information about who created the file, when, what software was used) also accumulates, though it's usually small.

When you compress a PDF, you're mainly telling the software to re-encode images at lower resolution and remove unnecessary data. The text itself barely shrinks because text is already compressed. This is why a PDF full of scanned pages shrinks dramatically, but a PDF that's mostly typed text may only shrink 10 to 15 percent.

Checking file size before and after compression

To see how much you've actually reduced the file, open Finder and navigate to the folder where you saved both versions. Right-click each PDF and select Get Info. The window that opens shows the file size in bytes, kilobytes, or megabytes. Compare the two numbers to see your compression ratio. If the compressed version is still too large, you can export it again with more aggressive settings.

Keep the original file in case you need it later — compression is not reversible. Once you've reduced a PDF, you can't restore the image quality by re-compressing it. If you ever need the original quality back, you'll need the uncompressed version.

Sharing compressed PDFs without losing important details

Before you send a compressed PDF to someone else, open it and scroll through to make sure text is still readable and images are still clear enough for their purpose. For forms, contracts, or documents that will be printed, test the compressed version on your printer first. For email or online sharing, the slight quality loss is almost never a problem.

If you're compressing a PDF that someone else created and you're not sure what it contains, ask them first. Some PDFs (like architectural drawings or medical images) need to stay high-resolution, and compression could make them unusable. For your own documents, you control the trade-off between size and quality.

Frequently Asked Questions

Can I compress a PDF that's already been compressed?

Yes, but the second compression usually shrinks it only a little more. Each time you compress, you lose some image quality, so compressing twice is not a good idea unless the first attempt was not aggressive enough. Start with stronger settings the first time instead.

Will compression make text blurry or hard to read?

Text usually stays sharp because text is vector-based (made of lines and curves, not pixels). Images get softer, but for most documents and forms, the difference is invisible on screen. If you're printing the PDF, test the compressed version first to be sure.

What if Preview's compression is not enough?

Try the manual quality sliders in Preview's export options and lower them more aggressively. If that does not work, a dedicated Mac app or web tool may compress more efficiently. You can also try removing pages you do not need before compressing.

Does compression work on PDFs from other people?

Yes, you can compress any PDF file you have access to. The compressed version is a new file, so the original stays unchanged. Some PDFs are password-protected and cannot be compressed without the password.

How small can I make a PDF?

That depends on what's in it. A text-only PDF may shrink only 10 to 15 percent. A PDF full of high-resolution photos can shrink 50 to 70 percent. There is a limit — you cannot compress below the actual data size of the text and lowest-quality images.