Given that Adobe Illustrator files _ARE_ PDF files and have been since AI 10...
Are you really sure of that???
AFAIK, the Illustrator native "language" is P
GF (Progressive Graphic Format), which is globally like PDF, but is in fact different (and not compatible)... The .AI file has a PDF structure, and PGF datas are embedded in this "PDF".
A "normal" .AI file, saved from Illustrator with the "Compatible PDF" option turned on contains both PDF and PGF datas, making this double-component file readable by some softwares, each software picking-up the datas it can read :
- Illustrator takes the PGF datas and ignores the PDF part,
- InDesign, Acrobat, Preview (and probably XPress 8) take the PDF datas and ignore the PGF datas...
... but an AI file "non pdf compatible" (meaning that the "Compatible PDF" option has been turned off when saving the .AI file) contains only PGF datas, no PDF datas, and only Illustrator can read such a .AI file. Meaning that it cannot be read by Acrobat, nor be imported in InDesign: as the .AI file has a PDF structure, beginning with "%PDF-version" like a "normal" PDF, Acrobat (and InDesign) believe that it is a "normal" PDF and open it, but they don't find any PDF datas, so they display a message (that you call the "instructional text") saying that they cannot use this "PDF-which-is-in-fact-not-a-PDF" because there is no PDF datas in it.
Only Illustrator (and InDesign) can read it's private information.
That's sure for Illustrator...
... but for InDesign, again, are you sure of that??? or is it a new feature of InDesign CS4 or CS5???
Because when I try to import a pure .AI file non-compatible PDF in InDesign CS3, the "instructional text") takes the places of the picture saying (approximative literal translation!) : "
This is an Adobe's Illustrator file that contains no PDF datas. To import this file, save it from Illustrator after having turned on the "Compatible PDF" option. etc."... meaning that InDesign is unable to read the natives Illustrator PGF datas of a pure Illustrator .AI file, and needs a double-component" PGF+PDF file to be able to use only the PDF part!
You are wrong...
What it does is create a PDF file _BUT_ instead of creating actual PDF page content that matches the Illustrator page content, it just puts some instructional text on the page.
Drag one on Acrobat to see....
The "instructional text" clearly says that the Illustrator file contains no PDF datas!
So, again, are you sure of what you say???
Again, AFAIK, when the "Compatible PDF" option is turned off, Illustrator creates a .AI file containing only the
PGF datas, but no PDF!
Again, you mix P
GF and P
DF: you should have wrote:
"What it does is create a P
GF file _BUT_ instead of creating actual PDF page content that matches the Illustrator page content, it just puts some instructional text on the page."