How to Compress a PDF on Mac (Built-in and Browser Methods)

Mac users have a built-in option for compressing PDFs via the Preview app, but it has a well-known problem: the results are often unpredictable. The Quartz filter can produce heavy compression artifacts, and in some cases it actually increases the file size rather than reducing it. For more reliable results, a browser-based approach gives you better control. Here is a clear comparison of both methods.

The built-in method: Preview's Quartz filter

macOS includes a PDF compression filter in the Preview app. Here is how to access it:

1. Open your PDF in Preview.
2. Go to File → Export as PDF.
3. At the bottom of the dialog, click the Quartz Filter dropdown.
4. Select Reduce File Size.
5. Click Save.

This is quick and requires no internet connection, which is its main advantage.

Why Preview's compression often disappoints

The Reduce File Size filter applies a fixed, aggressive compression regardless of the starting file or target use. The problems you may encounter:

• Over-compression, images in the document can come out looking blocky and blurry, even at relatively modest file sizes.
• Larger output than expected, for PDFs that contain primarily vector graphics or clean text, the filter sometimes produces a larger file than the original. This is a known quirk of the Quartz filter.
• No target size control, you cannot tell Preview to compress to, say, 5 MB. You get whatever the filter produces and have to check afterwards.
• Poor results on scanned documents, scanned PDFs can become unreadable when the filter is applied.

For casual use where quality does not matter much, Preview is fine. For anything going to a recruiter, a portal, or an official submission, the browser-based approach below is more predictable.

The browser method: PDFWhisk in Safari

PDFWhisk's compressor lets you set a specific target file size, 2 MB, 5 MB, 10 MB, or 25 MB, and compresses to that target rather than applying a one-size-fits-all filter. Here is how to use it on a Mac:

1. Open Safari and go to pdfwhisk.com/compress-pdf.
2. Drag your PDF from Finder directly onto the upload area in the browser window. This is faster than using the file picker, just have both Finder and Safari visible, then drag across.
3. Choose your compression target, select the size that matches your upload limit or intended use.
4. Download the result, the compressed file saves to your Downloads folder.

Processing happens in the browser using JavaScript and WebAssembly. Your file does not leave your Mac. Chrome and Firefox on macOS also work if you prefer them over Safari.

Using Automator for batch compression (advanced)

If you regularly need to compress large numbers of PDFs, macOS's Automator app can be set up to run a batch workflow. You can create a Quick Action that applies the Quartz filter to a group of selected files with a right-click. This is faster than processing one file at a time through Preview.

The steps:

1. Open Automator (found in Applications).
2. Create a new Quick Action workflow.
3. Set the workflow to receive PDF files in Finder.
4. Add the Filter PDFs action (search for "PDF" in the actions library) and configure it with the Reduce File Size option.
5. Add a Move Finder Items action to save the output to a folder of your choice.
6. Save the workflow with a name like "Compress PDFs".

Once saved, right-clicking any PDF (or group of PDFs) in Finder will show your Quick Action under the Services menu. Note that this still uses the Quartz filter, so the quality limitations above apply, but it saves time for batch work where consistency is more important than fine-tuned quality.

macOS sharing extension: a note on limitations

You may wonder whether you can use a "Share" button to send a PDF directly to PDFWhisk. The macOS Share extension (the share icon in Preview and other apps) only shows apps that have registered as share targets, and PDFWhisk is a browser-based tool, not a native macOS app. It will not appear in the share sheet.

The simplest workaround is to drag the PDF from Finder into the Safari browser window while PDFWhisk is open, or use the file picker in the tool. Both take a few seconds and are more reliable than trying to navigate the share sheet.

Which method should you use on Mac?

• Quick single-file compression, quality doesn't matter much → Preview → Export as PDF → Quartz filter
• Specific target size needed (e.g. under 5 MB for a portal) → PDFWhisk in Safari
• Batch processing multiple files → Automator Quick Action with Quartz filter
• Scanned documents or image-heavy PDFs → PDFWhisk (Preview will likely produce poor results)

For most practical document tasks, compressing a CV, preparing a file for portal upload, or reducing a scanned statement, open Safari, drag the PDF from Finder into PDFWhisk's compressor, and set your target. It takes less than a minute and gives you a predictable result.