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 needing to read anything. Open the PDF in Preview, go to File > Export As, then choose PDF from the format dropdown. Before you click Save, click Quartz Filter and select Reduce File Size. This compresses images and removes unnecessary data, often cutting the file to 30 to 50 percent of its original size.

The trade-off is visible: the PDF will look slightly softer or grainier, especially if it contains photographs or detailed graphics. Text usually stays readable. If the result is too blurry, you can undo and try again without the filter, or use one of the other methods below.

Key Takeaways

  • Preview's Reduce File Size filter is built into every Mac and works without installing anything, though it may make images look softer.
  • If you need more control over quality, macOS's ColorSync Utility lets you choose how much compression to explore before you save.
  • Online tools like Smallpdf and ILovePDF can shrink PDFs without downloading software, but they upload your file to their servers.
  • Dedicated Mac apps like PDF Squeezer and PDFtk offer batch processing if you regularly compress many PDFs at once.
  • The amount of shrinkage depends on what's in the PDF — text-heavy documents compress less than image-heavy ones.

Using ColorSync Utility for more control

If Preview's single filter is too aggressive or not aggressive enough, the ColorSync Utility gives you finer control. Open Preview, go to File > Export As, and before saving, click the dropdown next to Quartz Filter. Select Edit Quartz Filter. This opens ColorSync Utility with a list of compression settings you can adjust — image quality, resolution, and color depth.

Lowering the image quality slider reduces file size more but makes photos look worse. Reducing resolution (measured in DPI, or dots per inch) shrinks the file faster but can make the PDF blurry on screen or when printed. Most PDFs meant for screen viewing can drop to 72 DPI without looking obviously bad; printed documents usually need 150 DPI or higher.

After you adjust the settings, click Save As to create a new filter you can reuse. This is useful if you compress PDFs regularly and want the same settings each time.

Online tools that don't require installation

Websites like Smallpdf, ILovePDF, and Compressor.io let you upload a PDF and read a compressed version without installing software. You drag the file to the website, choose your compression level (usually Low, Medium, or High), and read the result. Most of these tools are free for one or two files per day.

The main drawback is privacy: your PDF is uploaded to their servers. If the PDF contains sensitive information — medical records, financial statements, or anything you would not want stored on someone else's computer — this method is not safe. Read the site's privacy policy to see how long they keep files and whether they use them for training their own tools.

These tools work on any computer with a web browser, including Windows and Linux, so they are useful if you need to send compressed PDFs to people on other operating systems.

Dedicated Mac apps for regular compression

If you compress PDFs often, a dedicated app may save time. PDF Squeezer (paid, around $20) and PDFtk (free, command-line tool) both let you compress multiple PDFs at once instead of one at a time. PDF Squeezer has a graphical interface where you drag files into a folder, set compression options, and let it process them all. PDFtk requires typing commands in Terminal, which is faster for people comfortable with the command line but slower to learn.

These apps run on your Mac, so your files never leave your computer. They also tend to offer more granular controls than Preview — you can set exact DPI, choose which elements to compress (images, fonts, metadata), and save custom presets.

Before buying, check whether the app is still actively maintained. Some PDF tools are abandoned and may not work on newer versions of macOS.

What affects how much a PDF can shrink

A PDF full of text compresses very little — maybe 5 to 10 percent — because text is already compact. A PDF full of high-resolution photographs can shrink by 70 percent or more because images take up most of the file size and compress easily. A mixed document (text plus some images) usually shrinks by 30 to 50 percent with standard compression.

Scanned documents (PDFs made from photographs of paper pages) compress well because they are essentially images. PDFs created from digital documents (like a Word file exported to PDF) may not compress much if the original was already optimized.

If a PDF is already compressed — for example, if someone else already ran it through a compression tool — compressing it again will not shrink it much further. You will see diminishing returns.

Checking file size before and after

To see how much space you saved, right-click the original PDF in Finder and select Get Info. Note the size listed under "Size". Then compress the file using any method above, right-click the new PDF, and check its size the same way. The difference tells you whether the compression was worth the quality loss.

If the compressed file is only slightly smaller than the original, the compression method was not effective for that particular PDF. Try a different method or accept that this PDF does not compress well.

When to compress and when to leave it alone

Compress a PDF if you are emailing it to someone with a slow connection, uploading it to a service with file size limits, or storing hundreds of PDFs on a device with limited storage. Do not compress if the PDF is a legal document, a contract, or anything where image quality or fine detail matters — the loss of clarity could cause problems later.

If you are unsure whether compression will cause problems, compress a copy and compare it side by side with the original. Look at any photographs, charts, or small text to see whether the quality loss is acceptable for your use.

Frequently Asked Questions

Will compressing a PDF make it unreadable?

No. Compression reduces image quality and file size, but the PDF remains readable. Text stays readable in almost all cases. Images may look slightly softer or grainier, but you can usually still see what they show. If the result is too blurry, you can undo and try a gentler compression method.

Can I compress a PDF that is password-protected?

Preview and most online tools will not let you compress a password-protected PDF without entering the password first. Open the PDF in Preview, enter the password when prompted, then follow the compression steps. Some dedicated apps have options to handle protected PDFs, but it depends on the app.

Does compressing a PDF change the original file?

No. Preview, ColorSync, and most other tools save the compressed version as a new file and leave the original untouched. Always check the filename before you save — if you save with the same name, it will overwrite the original.

What is the smallest file size I can get?

It depends on what is in the PDF. A text-only document might shrink only 5 to 10 percent no matter what you do. A photo-heavy document can shrink 70 percent or more. After one round of compression, compressing again usually does not help much — you hit a point of diminishing returns.

Is it safe to use online compression tools with confidential documents?

Online tools upload your file to their servers, so they are not safe for medical records, financial statements, or anything you would not want stored elsewhere. Use Preview or a dedicated Mac app instead, which keeps your files on your computer.