How to reduce scanned PDF file size on Mac

By | August 19, 2018

Problem: Reducing PDF file size on Mac

I scanned some of my personal documents in PDF format on Mac. The files were big sized for any email attachment and so I started looking for some application or free solution to reduce these PDF documents. The first solution that was readily available on my Macbook was to use Preview.

You can open a PDF document in preview mode and then select File–>Export. In export dialog select Reduce File Size for Quartz Filter and click save. A PDF file will be created by the specified name in export dialog with a minimal file size. However the export is not good for use as it substantially reduce the resolution and hence was not a good solution.

Then I stumbled across another simple and free solution by Jerome Colas. You need to download the below given filters and copy it to the appropriate location as per your OS.

Copy filters to below given location

  • If you are running Lion or Mountain Lion (OS X 10.7.x or 10.8.x) then you should put the downloaded filters in “Macintosh HD/Library/PDF Services”This folder should already exist and contain files.
  • If you are running an earlier version of OS X (10.6.x or earlier), then you should put the downloaded filters in “Macintosh HD/Library/Filters”.

How to use these filters

  • Open a PDF file using Apple’s Preview app,
  • Choose Export (or Save As if you have on older version of Mac OS X) in the File menu,
  • Choose PDF as a format
  • In the “Quartz Filter” drop-down menu, choose a filter “Reduce to xxx dpi yyy quality”“Reduce to 150 dpi average quality – STANDARD COMPRESSION” is a good trade-off between quality and file size

Screenshots are given below


Actual File Size


Enter export as name, select filter from Quartz Filter


Selected Standard compression 150 dpi


Actual and reduced file sizes

Here is how it works:

    • These are Quartz filters made with Apple Colorsinc Utility.
  • They do two things:
    • Down sample images contained in a PDF to a target density such as 150 dpi,
    • Enable JPEG compression for those images with a low or medium setting.
  • It works with most of the PDF files however their are exceptions. The details are given below: –
      • It will generally work very well on unoptimized files such as scans made with the OS X scanning utility or PDFs produced via OS X printing dialog.
      • It will not further compress well-optimized (compressed) files and might create bigger files than the originals,
    • For some files it will create larger files than the originals. This can happen in particular when a PDF file contains other optimizations than image compression. There also seems to be a bug (reported to Apple) where in certain circumstances images in the target PDF are not JPEG compressed.

Leave a Reply

Your email address will not be published. Required fields are marked *