The fastest way: use Preview, the app already on your Mac

Open the PDF in Preview (the default app when you double-click a PDF). Go to File in the menu bar, then select Export. A dialog box opens. Near the bottom, you will see a dropdown that says Quartz Filter. Click it and choose Reduce File Size. Then click Save.

This method works because Preview uses built-in compression filters that shrink PDFs by removing redundant data and lowering image quality slightly. The file size usually drops by 30 to 50 percent. The trade-off is that images inside the PDF become less sharp, especially if you zoom in or print the document. Text stays readable.

If the Quartz Filter dropdown does not appear, your version of macOS may be older. You can still compress by going to Tools in the menu bar, looking for Optimize PDF, and clicking that instead. The result is similar.

Key Takeaways

  • Preview's Reduce File Size filter is built into every Mac and compresses most PDFs by 30 to 50 percent without extra software.
  • The compression trade-off is lower image quality; text remains clear, but photos and graphics become less sharp.
  • For PDFs with many high-quality images, you may need to choose between smaller file size and keeping image detail.
  • If you need to compress many PDFs at once, Automator can run the same compression on a whole folder without opening each file.

When the Reduce File Size filter is not enough

If Preview's standard compression does not shrink the file as much as you need, try the Reduce File Size (Extreme) filter instead. This setting compresses more aggressively and can cut file size by 50 to 70 percent, but images will look noticeably grainier. Open the PDF in Preview, go to File > Export, click the Quartz Filter dropdown, and select Reduce File Size (Extreme).

The extreme setting is useful if you are sending the PDF over email with a strict size limit, or storing many PDFs on a device with limited space. It is less useful if the PDF contains charts, diagrams, or photographs that need to stay legible. Test it on a copy first to see whether the quality loss matters for your document.

Compressing PDFs with many images or graphics

If your PDF is large because it contains many photographs or detailed graphics, Preview's filters may not give you the control you need. In that case, you have two options: use a dedicated compression tool, or manually reduce image quality before creating the PDF.

For a dedicated tool, PDF Squeezer 4 and PDFtk Pro are Mac applications that let you choose how much to compress images and which parts of the PDF to leave untouched. Both cost money (usually $10 to $30) and are worth it only if you compress PDFs regularly. You can also use free online tools like Smallpdf.com or ILovePDF.com, but uploading to a website means your PDF leaves your computer, which matters if the document contains sensitive information.

The manual route is slower but gives you the most control: open the original document (Word, Google Docs, or whatever you used), reduce the size or quality of the images inside it, then export to PDF again. This way you avoid compressing an already-compressed file, which often produces worse results than compressing once from the start.

Using Automator to compress multiple PDFs at once

If you have many PDFs to compress, you can set up a straightforward Automator workflow that does the work for you. Open Automator (in Applications > Utilities). Create a new document and choose Quick Action as the document type. Search for the action called explore Quartz Filter to PDF Documents and drag it into the workflow.

In the filter dropdown, select Reduce File Size. Save the workflow with a name like "Compress PDF". Now you can right-click any PDF (or a folder of PDFs), select Quick Actions, and choose your workflow. Automator will compress all selected files and save them with "_Reduced" added to the filename, leaving your originals untouched.

This approach saves time if you regularly compress PDFs, but it applies the same filter to every file. If some PDFs need extreme compression and others need to keep image quality, you will still need to handle them separately.

What happens to your PDF when you compress it

Compression works by finding patterns in the file and storing them more efficiently. For text-heavy PDFs, this means almost no visible change — the words stay sharp and the file shrinks significantly. For image-heavy PDFs, compression removes some of the color information and detail in photographs, which is why images look softer or grainier after compression.

The compression is permanent once you save. You cannot undo it by opening the compressed file again, so always keep a copy of the original if you might need the high-quality version later. If you compress a PDF that is already been compressed (for example, a PDF you received from someone else and then compressed again), the quality loss compounds and the file may not shrink much further.

Deciding which compression method to use

Use Preview's Reduce File Size if the PDF is mostly text, or if you need a quick result and do not mind slightly softer images. This is the right choice for most people most of the time.

Use Reduce File Size (Extreme) if file size is the priority and the PDF is going to be read on screen (not printed), or if image quality does not matter much.

Use a dedicated tool or manual re-export if the PDF contains important photographs or graphics that need to stay sharp, or if you need fine control over what gets compressed.

Use Automator if you compress PDFs regularly and want to save time on repetitive work.

Frequently Asked Questions

Can I compress a PDF without losing any quality?

No. All compression involves some trade-off. Preview's filters are designed to remove data that humans notice less (like fine detail in images), but something is always lost. If quality cannot change at all, the file size will not shrink much. You have to choose which matters more for your situation.

Will compression make my PDF unreadable?

No. Text stays readable even with extreme compression. Images become grainier, but you can still see what they are. If readability is your concern, Preview's standard Reduce File Size filter is safe for almost any document.

How much smaller will my PDF get?

It depends on what is inside. Text-heavy PDFs shrink by 30 to 50 percent. PDFs full of high-quality photographs can shrink by 50 to 70 percent with extreme compression. Some PDFs (especially those already compressed) may shrink by only 10 to 20 percent no matter what you do.

What if I compress a PDF and it is still too large?

Try the Extreme filter instead of the standard one. If that does not help enough, the PDF may contain very large images or embedded files. In that case, you need either a dedicated compression tool that lets you resize images, or you need to go back to the original document and reduce image sizes before creating the PDF again.

Is it safe to upload my PDF to an online compression tool?

Online tools are convenient but your file travels to someone else's server. If the PDF contains private information (medical records, financial statements, legal documents), use Preview instead. If it is a public document or a file you do not mind sharing, online tools are faster and sometimes offer more control over compression settings.