How to Compress PDFs on macOS Without Losing Quality

Ben Stegner 02-12-2016

While there’s plenty of awesome Mac software The Best Mac Apps to Install on Your MacBook or iMac Looking for the best apps for your MacBook or iMac? Here's our comprehensive list of the best apps for macOS. Read More , some of the best you can use comes pre-installed on your computer The Best Default Mac Apps That You Shouldn't Need to Replace Here are some of the best default, pre-installed, native Mac apps worth using. Don't ditch them before you try them! Read More . One of these tools is Preview, macOS default image and PDF viewer.


One of the little-known features of Preview is that it can shrink the size of PDFs. To do so, open a large PDF in Preview and click File > Export. In the Quartz Filter drop-down box, select Reduce File Size to make it smaller. The problem with this method is that it can make the files way too small, and make them so blurry that they’re unreadable.

If you’d like to go hands-on, you can make a few edits to the XML files that control this behavior. Use Finder to browse down to /System/Library/Filters. Find the file called Reduce File Size.qfilter and copy it to your desktop. If you like, you can create multiple copies of this file, and give yourself several compression options.

Right-click it and choose Open With > TextEdit, or whatever your preferred text editor is.

Look for the Compression Quality field. By default, this is set to 0, but can be set to any number between -1 (most compressed) and 1 (least compressed). If you’re creating multiple files, try setting one of these to 0.50 (medium quality) and one to 0.75 (high quality).

The other field to check is ImageSizeMax. By default, this is set to 512, but you can increase it to increase the final size. Try setting this to 1684 for your medium quality compression (resulting in A4 at 144 DPI), and 3508 for the high quality compression (A4 paper at 300 DPI).


Finally, look for the Name field in each one. Change this to something self-evident, as it’s what will appear in the Quartz Filter drop-down later. Name the files to match these names, and copy/paste them back into /System/Library/Filters. This will add new options for compression to your Export menu. If you don’t like the suggestions above, try playing with the values a bit!

If you don’t want to go through these steps, try a free browser tool like SmallPDF to compress your PDFs How to Compress a PDF, Reduce the File Size, and Make It Smaller This guide covers how to make a PDF smaller and manually reduce its size using simple programs and tools. Read More .

Do you often compress PDFs on your Mac? Let us know if this method was useful for you!

Image Credit: ibreakstock via Shutterstock

Related topics: File Compression, PDF.

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