The fastest way to shrink a PDF on Mac

The built-in Preview app on your Mac can reduce a PDF's file size without requiring any additional software. Open the PDF in Preview, go to File > Export, choose PDF from the format dropdown, and click the Quartz Filter dropdown to select "Reduce File Size". This single step typically cuts file size by 30 to 50 percent, depending on the original content.

If the result is still too large, you have other options built into macOS that work differently — some strip out images entirely, others compress them more aggressively. The trade-off is always the same: smaller file size means lower image quality and less detail in charts, photos, or scanned documents.

Key Takeaways

  • Preview's "Reduce File Size" filter is the fastest method and works for most PDFs without opening additional apps.
  • Quartz Filters in Preview let you choose how aggressively to compress, trading quality for size depending on your needs.
  • For scanned documents or image-heavy PDFs, compression works better than for text-only files.
  • If Preview's built-in options are not enough, third-party apps like PDFtk or Automator workflows offer more control over what gets removed.

Using Preview's Quartz Filter options

Preview offers three Quartz Filter choices when you export a PDF. "Reduce File Size" is the gentlest option and works well for most documents. "Lighter Quartz Filter" compresses more aggressively and is useful when you need the file smaller but still readable. "Remove Black Borders" is designed specifically for scanned documents and strips the dark edges that scanners often capture around the page.

To use any of these: open your PDF in Preview, click File, select Export, make sure PDF is chosen as the format, click the Quartz Filter dropdown, pick your filter, and click Save. The app will process the file and save a new version. Your original stays unchanged.

The difference between filters is noticeable mainly in image-heavy PDFs. A text-only document might shrink only 10 to 15 percent even with aggressive compression, because there is little to compress. A PDF full of photographs or scanned pages can shrink 50 to 70 percent.

When to use Automator for batch compression

If you have multiple PDFs to shrink, Automator — Mac's built-in automation tool — can compress them all at once. Open Automator from Applications > Utilities, create a new Quick Action, search for "PDF" in the actions library, and drag "Reduce PDF File Size" into your workflow. Set it to save the compressed files to a folder you choose, then save the action with a name like "Compress PDFs".

Once saved, you can right-click any PDF or folder of PDFs in Finder, select Quick Actions, and run your compression action. This saves time if you regularly shrink documents. The compression uses the same method as Preview's "Reduce File Size" filter, so results are identical.

Automator is worth learning if you compress PDFs weekly or more often. For one-off files, Preview is faster because you do not need to set up the workflow first.

Third-party apps for more control

If Preview's filters do not shrink your PDF enough, apps like PDFtk, Ghostscript, or dedicated PDF compressors offer finer control. These tools let you set specific compression levels, remove embedded fonts, strip metadata, or delete images entirely. They are more complex to use than Preview but give you options when the built-in tools are not enough.

Most of these apps cost money or require command-line knowledge. Before buying, try Preview's "Lighter Quartz Filter" first — it handles 80 percent of compression needs. Only move to a third-party tool if you regularly work with PDFs that Preview cannot shrink to your target size.

Why file size matters and what you are trading away

Smaller PDFs upload faster, take less storage space, and are easier to email. But compression always removes data. Images become blurrier, fine details in charts disappear, and scanned text can become harder to read. A PDF compressed for email might be unreadable when printed at full size.

Before you compress, ask what the PDF will be used for. If it is a contract you are emailing to a lawyer, keep it uncompressed — they need to read every word clearly. If it is a reference document you are archiving, compression is fine. If it is a scanned receipt, aggressive compression barely matters because the original is already low quality.

Checking file size before and after compression

To see how much space you saved, right-click the original PDF in Finder and select Get Info. Note the file size. Then right-click the compressed version and do the same. The difference shows you what compression achieved. If the compressed file is only slightly smaller, the original probably had little to compress — usually because it was already a text-only PDF with no images.

If compression did not shrink the file as much as you hoped, the PDF likely contains embedded fonts, metadata, or other non-image data that Quartz Filters do not touch. In that case, a third-party tool designed to strip those elements might help, but the gain is usually small.

Frequently Asked Questions

Can I compress a PDF without losing quality?

Not completely. Compression always removes some data — the question is whether you notice. Text-only PDFs shrink with almost no visible loss. Image-heavy PDFs show blurriness or loss of detail. Preview's "Reduce File Size" filter is the gentlest option and usually keeps quality acceptable for screen viewing.

Why did Preview's compression barely shrink my PDF?

PDFs that are mostly text do not compress much because text takes very little space. If your PDF is already optimized or contains no images, Quartz Filters have little to work with. Compression works best on scanned documents and PDFs full of photographs.

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

Yes — Preview saves the compressed version as a new file and leaves your original untouched. If the compressed version is too blurry or low quality, delete it and use the original. You can always try a different Quartz Filter on the original.

Is there a way to compress without opening Preview each time?

Yes, use Automator to create a Quick Action that compresses PDFs with one right-click in Finder. This is faster if you compress multiple files regularly, but takes a few minutes to set up the first time.

What if I need the PDF smaller but Preview is not compressing enough?

Try Preview's "Lighter Quartz Filter" instead of "Reduce File Size" — it compresses more aggressively. If that is still not small enough, you likely need a third-party tool that can remove embedded fonts or metadata, though the gain is usually modest.