Why should you use the Create PDF compatible file option when saving as Illustrator file in Adobe® Illustrator®?
An Adobe® Illustrator® file (.ai) consists of two parts:
The “Illustrator high level information” part: Only Adobe® Illustrator® is capable of reading this information, so it is of no use to other applications.
The “PDF part”: Esko software needs this in order to correctly process an Adobe® Illustrator® file. This part is only available when the Create PDF compatible file option is activated during a Save as operation.