I’ve touched on this before, but it bears repeating: InDesign is the Swiss Army Knife of PDF file size.

Behold, a section of the new Notre Dame Campus Map file that I am currently building in Illustrator:

Saving this as a PDF at the default file size results in a 2M+ file. Reducing the setting to “Smallest File Size” still comes in at around 1M.

InDesign allows you to further reduce this file size if you create a new document and place the .AI file as a standard graphic, then Export using Cmd+E. Select “Smallest File Size” from the settings menu. In this case the result takes a standard illustrator PDF from 2M to around 800K, or less then half of the original file size…all the better for emailing, especially over slower internet connections.

This works because InDesign basically creates a “flat” image of the placed graphic and then outputs it to PDF. Along the way, this process sheds extra vector data and in the case of layered Photoshop files, extra non-visible image data from hidden layers that adds complexity and file size to your PDF unnecessarily. The concept works to reduce the “weight” of any large image file.

I use this hack all the time to reduce PDF file size. In this earlier article I discuss how I use InDesign and Photoshop together to tame even larger PDFs with file sizes in the hundreds of megabytes.