How to Compress PDFs on macOS Without Losing Quality
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!
Do you often compress PDFs on your Mac? Let us know if this method was useful for you!
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