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    How to reduce PDF file size without losing quality on Mac

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    Pau Monfort
    @paumonfort

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    Here is a way to reduce the size of PDF files on your Mac without losing too much quality. When sharing a PDF file via email or keeping it in cloud storage, it makes sense to keep the file as small as possible so as not to waste space. On a Mac, you can use the built-in Preview app to resize PDFs, which is handy.


    However, this process is not perfect as it significantly reduces the quality of the file. We will show you how to reduce PDF file size without losing quality on a Mac.



    How to convert Word to PDF on MAC, Windows, Android and iPhone

    How to resize PDFs in Preview on Mac

    It's easy to reduce the size of a PDF using Preview. To do this, double-click a PDF in the Finder to open it in Preview. Once uploaded, select File> Export from the menu bar at the top of the screen. In the resulting window, open the drop-down box Quartz filter and select Reduce file size before exporting the file, which will shrink it.

    While this provides a smaller file size for the PDF, the problem with this method is that it drastically reduces the quality of the file. If your PDF gets so blurry that it's unreadable, that's not a suitable solution.


    Thankfully, you can edit some files on your Mac to find a better balance between quality and file size. However, this requires disabling important security protection on modern versions of macOS.

    Disable SIP to change the PDF export quality

    Starting with OS X El Capitan in 2015, Apple introduced System Integrity Protection (SIP). This increases the security of your Mac by limiting access to sensitive folders on your device. Unfortunately, you need to access the protected folder /System to make this change to the PDF.



    If you feel comfortable, you can disable System Integrity Protection to proceed with the following steps. If you do, be sure to re-enable SIP as soon as you're done to keep your Mac safe. You should also avoid downloading untrusted software while you have SIP turned off.


    In case you don't want to follow these steps, there are easier ways to reduce the PDF file size without losing quality. Web tools are your best option; try a free service like SmallPDF to reduce PDF file size without downloading anything.

    How to reduce PDF file size on Mac without losing quality

    To change the necessary system files after disabling SIP, first open Finder. Select Go> Go to folder from the menu bar, then enter the location / System / Library / Filters.

    The contents of the resulting folder controls the options available in the drop-down menu Quartz Filter mentioned earlier. You should see one called Reduce File Size.qfilter. Copy this and paste it on your desktop or other convenient location.


    To give you more PDF compression options, create multiple copies of the file Collapse size file.qfilter. By changing the underlying values ​​differently for each and saving them all separately, you can access various compression levels from the same menu.

    Edit PDF quality file

    Now, right click on the duplicate file you just created. You choose Open with> TextEdit or whatever your favorite text editor is. It opens as an XML file, which is a common format for saving program options in a way that both people and machines can read and understand.


    Within this file, look for the line Compression quality, which is located inside of the tag . You can press Cmd+F to search for it if necessary. By default, the value below this line, in the tags , is set to 0.0. However, it can be set to any value between -1 (maximum compression, minimum quality) e 1 (minimum compression, best quality).


    You may need to change this value a few times to find the right balance between quality and file size. Trial 0,5 for medium level compression - you can adjust it later if it doesn't feel right. If you're creating multiple files for varying levels of compression, give it a try 0,75 for a higher quality file.

    Still within the XML file, the next field to check is ImageSizeMax. By default, it is set to 512, but you can change it to increase the final size after compression. Try setting it to 1684 for medium quality compression (results in A4 size paper at 144 DPI) e 3508 for high quality compression (equivalent to A4 paper at 300 DPI).

    Finally, look for the field Your name at the bottom of the file. Change it to something clear, as the name will appear in the drop-down box Filter al quartz when you have finished. If you are creating two new files, you can use Reduce file size better for that of medium quality e Reduce file size better for the high quality option.


    Added new PDF export options to the preview

    Save each file when done. Rename the files in Finder to match the names you gave them in the XML, then copy and paste them back into / System / Library / Filters from where did you get the original file. If that doesn't work, make sure you've disabled SIP, as you can't move files to this folder when it's active.

    Now when you use the menu Export In Preview, you will see the new compression options in the dropdown menu quartz filter. Use them to create a smaller PDF that doesn't drop in quality as much as the default setting.

    If you don't like the look or the file size is still too big, try playing around with the values ​​a bit until you get them right. Remember to re-enable SIP once you are happy with the new export options.


    Compress PDF Mac without losing quality

    Now you know how to reduce the file size of a PDF in macOS without making it completely blurry. Disabling SIP is an intensive step, so you may not want to do all of this if you just need to resize PDFs occasionally. But if you always use the option in Finder, having the best quality options in the same menu comes in handy.

    Don't forget that you can do a lot more with PDFs on your Mac!

    Further Reading:

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    • How to reduce the size of a JPEG: 5 ways
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