How to compress PDF for free on your Mac

I’m sure you’ve encountered this situation before. You scan a document with your scanner and save it as a PDF document. And when you need to send it over as an attachment in an email, lo-and-behold, you realises that the scanned document is about 7.86MB large! Just for a grayscale document? Then you remembered that you might have set the scanner’s settings to 600 DPI. Oops. Now, you need to figure out how to scale the document down to a reasonable size. You wonder if you can compress PDF for free on your Mac or if you have to pay for a utility to do that.

The 5 seconds (Lazy) option: Pay for and use a PDF compression utility

Not a bad option really. A quick search on the Mac App Store shows there are quite a number of apps that does exactly this, such as the $3.99 PDF Squeezer app that seems to have some positive reviews on the App Store.

If you don’t want to get you hands a little dirty and can easily afford $3.99 on an app, this really is a good option.

The 5 minutes (cheapskate) option: Compress PDF for free with utilities already on your Mac

But of course, if you are continuing to read on, you really want to just compress PDF for free. As you probably already know, the Preview app on the latest OS X version, El Capitan, is rather powerful. Though not exactly Adobe Acrobat level of capability, but it’s so far not failed to meet my needs in terms of manipulating a PDF document, with the only exception of compressing or optimising a PDF document.

So, let’s get on to it. Here’s how you would get it all to work.

To start, let me introduce you to a utility called ColorSync. Long story short, ColorSync is a utility that ships with your Mac that is used for management of color profiles and also the management of Quartz filters which you can modify your colors or add effects to your PDF files and other documents. Now that, last bit there about the Quartz filters, that’s the interesting bit that allows you to do cool stuff on your PDF documents. But if you want to first know more about ColorSync, you can read it here in this old article on Apple’s support page: https://support.apple.com/kb/ph6826?locale=en_US

To launch ColorSync, just simply use Spotlight or Launchpad and simply search for it.

Once you launch it, you should see the following screen. Click on the Filters icon as that’s what we are interested with for this trick.

Now that you’re in the Filters section, let’s create the Quartz filter! For this tutorial, I would be creating a filter that would reduce the DPI of the PDF down to 150 and then compress the PDF pages using JPEG compression at about 80+% quality. This should bring down the size of a large PDF quite significantly.

Step 1: Create a new filter by clicking on the + button at the bottom left. You should see a new untitled filter created. Rename it with something meaningful and press “Enter” to confirm it. If the name isn’t right, just double-click on the filter again and edit it to your liking.

Step 2: Add in the filters that you want to be applied on to the PDF document. Firstly, let’s add a Color Image Sampling filter and set the downsampling to 150 DPI.

Step 3: Let’s add another filter, this time to compress the PDF image with JPEG compression at about 80+% quality.

At this point, you now have a ready Quartz filter you can use with Preview! But if you want to create more filters, keep repeating the steps above and configure different compression and optimisation options based on your needs. For me, I simply created a Color and Grayscale version of the filter above.

Now, the next thing you need to do is to move the filter from the /Users/<username>/Library/Filters folder to the /Library/PDF Services folder. The tricky part here, if you don’t already know, is that the Library folder is hidden in Finder. So, you will need to use the Go To Folder option and go to “~/Library/Filters” and then open another Finder tab or window and go to “/Library/PDF Services”. Then, just copy over the filters you created in the Filters folder and move them into the PDF Services folder.

Do note that you will need to authenticate the file movement as the “/Library/PDF Services” folder is a system folder.

Once that’s done, it’s now time to test the filters in Preview. It so happens that I have a 16.8MB PDF on my MacBook, so let’s see what happens when we apply the filter to it. In order to apply the filter, all you need to do is open the PDF in Preview, select the Export option in the File menu and then choose the Quartz filter you created in the Export options.

Wow. The filter shed off 11.2MB from the original file. That’s a whopping 66% reduction in file size! This filter is a definitely keeper in my books. ? I hope you would find this tip useful too and start to compress PDF for free on your Mac.