The fastest way: use Preview to reduce file size

The simplest path on a Mac is Preview, the built-in app that opens PDFs by default. It can shrink a PDF to roughly half its original size in under a minute, with no quality loss noticeable to most readers. You do not need to read anything or learn new software.

Open your PDF in Preview. Go to the menu bar and click File, then Export As. A dialog box opens. At the bottom, you will see a dropdown that says Quartz Filter — click it and select Reduce File Size. Then click Save. Preview creates a new, smaller PDF without touching the original.

The trade-off is small: Preview's compression works best on PDFs with images or scans. Text-heavy PDFs compress less noticeably because they are already lean. If your PDF is mostly words, you may see only a 10 to 20 percent reduction. If it contains photos or scanned pages, expect 40 to 60 percent.

Key Takeaways

  • Preview's Reduce File Size filter is built into every Mac and compresses most PDFs to half their original size without requiring any downloads.
  • The compression works by lowering image resolution inside the PDF, so it is most effective on files with photos or scans rather than plain text.
  • You can also compress by exporting to a different format — saving as PDF/X or using the Print dialog — if Preview's standard filter does not shrink the file enough.
  • Third-party apps like ColorSync Utility offer more control over compression settings if you need to fine-tune quality versus file size for specific documents.

Using the Print dialog for additional compression

If Preview's standard compression does not shrink your PDF enough, the Print dialog offers another route. Open your PDF in Preview, click File, then Print. In the dialog that opens, look for a dropdown near the bottom left that says PDF. Click it and select Save as PDF.

A new save dialog appears. Before you save, look for an Options or Settings button — the exact label depends on your macOS version. Click it to see compression choices. You can lower the image quality slider or change the compression method. Save the file with a new name so you keep the original.

This method gives you more control than Preview's one-click filter, but the results are often similar. Use it when you want to experiment with different quality levels before settling on a final version.

Compressing with ColorSync Utility for precise control

If you need finer control over how much compression happens, ColorSync Utility is built into every Mac and offers more options than Preview. Open Spotlight (press Command + Space), type "ColorSync Utility," and press Enter.

In ColorSync Utility, click Filters in the top menu. You will see a list of filters on the left, including several compression options. Select one — Reduce File Size is the most common — then click the gear icon at the bottom to edit it. You can adjust image resolution, compression quality, and other settings. Once you have configured it, go back to Preview, use File > Export As, and select your custom filter from the Quartz Filter dropdown.

This approach takes longer but lets you compress multiple PDFs the same way without repeating the settings each time. It is worth learning if you compress PDFs regularly.

When compression is not enough: splitting large PDFs

Some PDFs stay large even after compression — usually because they contain high-resolution images or many pages. If you need to send the file by email or upload it somewhere with a size limit, splitting it into smaller pieces may work better than further compression.

Preview can do this too. Open your PDF, click View in the menu bar, and make sure Thumbnails is checked. A sidebar appears showing every page as a small image. Click and drag to select the pages you want to extract, then go to File > Export As and save them as a new PDF. Repeat for the remaining pages. You now have two or more smaller PDFs instead of one large one.

This works when the recipient can open multiple files, but it is less convenient than a single compressed document. Try compression first; split only if compression does not shrink the file enough.

Checking your file size before and after

To see how much space you actually saved, find the PDF in Finder. Right-click it and select Get Info. Look for the line that says Size — this is the file size in bytes, kilobytes, or megabytes. Write this number down or take a screenshot.

Now compress the PDF using one of the methods above. Find the new compressed PDF in Finder, right-click it, and select Get Info again. Compare the two sizes. If the reduction is not enough, try a different compression method or adjust the settings in ColorSync Utility.

Most people find that Preview's default compression is sufficient. If your PDF is still too large after that, the file probably contains images that are genuinely important to keep at high quality — in which case further compression may make them blurry or hard to read.

Avoiding common compression mistakes

The most common mistake is compressing a PDF multiple times in a row, thinking each pass will shrink it further. It will not. Once Preview or ColorSync has compressed a PDF, running the same compression again produces almost no additional reduction. If you need more compression, change the method or settings instead of repeating the same one.

Another mistake is compressing a PDF that contains important images or charts, then realizing the compressed version is too blurry to read. Always keep the original file. When you export or save as a new PDF, give it a different name — something like "filename-compressed.pdf" — so you still have the original to fall back on.

Do not compress a PDF that someone else will need to print or edit. Compression lowers image resolution, which can make printed copies look grainy. If you are unsure whether the recipient needs the original quality, send the uncompressed version or ask first.

Frequently Asked Questions

Will compression make my PDF blurry?

Compression lowers the resolution of images inside the PDF, so text and straightforward graphics stay sharp, but photos and detailed images may look slightly softer. For most documents sent by email or viewed on screen, the difference is not noticeable. If your PDF contains important photos or artwork, test the compressed version before sending it to someone else.

Can I undo compression if I do not like the result?

No — compression is permanent once you save the new file. That is why you should always save the compressed version with a new name and keep the original. If the compressed version does not work, you still have the original to try again with different settings.

Why is my PDF still large after using Reduce File Size?

Some PDFs contain images that are already compressed, or they use fonts and graphics that do not compress well. If Preview's filter does not shrink the file much, try ColorSync Utility to adjust the image quality slider lower. If it is still large, the file may genuinely need that size to maintain readability.

Is there a way to compress a PDF without opening it?

Yes — you can drag and drop a PDF onto Preview in the Dock, then use File > Export As with the Reduce File Size filter. Some third-party apps also accept drag-and-drop, but Preview is the fastest built-in option.

What is the difference between Preview and ColorSync compression?

Preview offers one standard compression setting that works for most PDFs. ColorSync lets you adjust image quality, resolution, and other settings before compressing. Use Preview for quick compression; use ColorSync if you need to fine-tune the result or compress many PDFs the same way.