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Vector graphics is a compact way of storing simple drawings. And I always thought that the most compact .pdf file you can get from Illustrator, is achieved with the "Smallest file size" preset. However, I have recently discovered that a .pdf saved from Illustrator with this preset or any other I have tried so far is very large compared to what Inkscape can produce.

For example, here is the same simple picture drawn in Illustrator and Inkscape and saved in the .pdf format with minimal settings. It is easy to see that while the Illustrator .pdf is 37.3 Kb, the Inkscape .pdf is 3.2 Kb, which is 10 times smaller! An enormous difference!

So, the question is why the "Smallest file size" setting of Illustrator makes such huge files and can Illustrator .pdf files be made much smaller (because I have found myself recently making figures in Illustrator, saving as .svg and making a .pdf in Inkscape)? And what on Earth does Illustrator write in those .pdf's?

Here is an .svg picture which can be open in both Illustrator and Inkscape in case someone wants to try. And I put her a .png picture just in case my uploaded files are no longer accessible: .png picture in question

  • Are you deleting all unnecessary library items (swatches, brushes, symbols, etc) before saving? Subsetting fonts? This is more about the PDF job options in Illustrator and its settings than it is about Illustrator specifically. "Smallest File size" is a guess by Adobe, but it can be changed. – Scott Apr 2 '15 at 22:02
  • Also, be sure to uncheck illustrator compatible file or the pdf will in fact become a pdf+ a illustrator file embedded. – joojaa Apr 10 '15 at 5:14
  • @Scott So I actually have to remove all swatches and brushes every time before I save a pdf document to make it smaller? – Dr_Zaszuś Apr 10 '15 at 8:29
  • Generally, yes. There is an action to "Delete Unused Items" Just run the action before saving. – Scott Apr 10 '15 at 8:49
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It's a whole bunch of metadata, including embedded JPEG thumbnails: enter image description here

You can open that PDF in a text editor and delete the entire block if you want, and the PDF still works:

https://www.dropbox.com/s/l7saorb5zcxr3mf/stripped%20metadata.pdf?dl=0 (about 6kB)

Or you can run it through Acrobat Pro and do the "Sanitize" command, which makes it even smaller (about 2kB, similar to Inkscape's output). You can automate this through an Acrobat action if you'd like.

Or you could perhaps try a commercial product that can batch remove them from all your files. I never used it, but here's one Google found: http://www.digitalconfidence.com/BatchPurifier.html

  • Thank you, very interesting. I didn't know about the existence of the "Sanitize" command. It works well, I found also that the resulting size is somewhat equivalent to the one you obtain with the "Optimize PDF" command and unchecking the unnecessary elements. However, the Inkscape ouput pdf is still smaller... – Dr_Zaszuś Apr 10 '15 at 8:27
  • If I open the file with a text editor (e.g., WordPad), it doesn't recognize the encoding of the document... – Dr_Zaszuś Apr 10 '15 at 8:29
  • Interesting... with my version of Acrobat, Sanitize brought your sample file down to 2kB, far smaller than the Illustrator optimized output. As for editing it manually, use Notepad instead of Wordpad or download the free Notepad++. WordPad isn't so much a text editor as much as lightweight word processor, the difference being WordPad will try to read all that binary data as font formatting information, whereas a proper text editor just shows you the raw data so you can make the changes you need to. I like Sublime Text myself, but it's not free. – arcataroger Apr 17 '15 at 3:36

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