In that case, perhaps someone should explain that to Adobe.
Don't assume your interpretation of the Adobe help files is correct, or that just because an Adobe document uses the words "layer" and "PDF" in the same paragraph, it means what you say it means. "Layered content" is a conceptual description, not an analogue to the physical layers in some Adobe native-format documents.
And yes, part of my professional life is indeed explaining things to Adobe. As I said, I used to teach the people who now work for them, and I'm on speaking terms with the founder of the company. What is it you do for a living again? What is your personal expertise on this subject?
"PDF files can contain layered content...
But practically never do.
Why? Because the PDF document-structure data structures don't directly support it. You have to slightly violate the PDF object inheritance model and page-layout and object-grouping models, and therefore the option that directs Adobe's PDF exporters to attempt to reproduce the original InDesign document layers is disabled (not just unchecked, but turned off altogether) by default. The
ExportLayers option in the low-level Adobe configuration for InDesign ships with it set to "ExportVisiblePrintedLayers," and it takes a bit of ingenuity to reset it. I managed just now to set it to "ExportAllLayers," but an ordinary user isn't going to know how to do this, nor would have any motive to do so. And
still, InDeign's log for PDF export reported "Flattening layers..." as part of the export, and produced a flat PDF file (see below).
...if they are created from layered documents by using applications such as Adobe InDesign.
Yes, you posted this paragraph before and I answered it before. I'll answer it again, in more detail.
First,
only InDesign supports the layer-export option. Illustrator and Photoshop do not. Birther pseudo-expert Mara Zebest claims Photoshop was used. If you want to claim InDesign was used instead, you'll have to repudiate Zebest. Make your choice and stick with it.
Second, there's a glaring difference between PDFs produced by Adobe InDesign, and PDFs produced by Apple's QuartzPDF -- including the Obama PDF. Actually there are several, but I'll only ask you for one.
Please tell us what that glaring difference is that would enable an expert immediately to determine that it had been created with one and not the other. I'll bet you can't do this.
Third, the InDesign layer export is supported only for PDF 1.4 and later.
The Obama PDF is 1.3. Most of the Adobe products allow you to select the PDF compatibility level for your export. If you choose 1.3, the document is flattened regardless of
ExportLayers setting.
Fourth -- and most important, the mechanism referred to has
absolutely nothing to do with the fact that Birther "experts" pointed to straightforward PDF
objects in a flat, unstructured PDF file and ineptly mistook them for "layers." That's just a
huge pile of stupid, which is why none of the Birther "experts" pass
voir dire in court. If an equestrian "expert" at the racetrack points to a shoeshine box and calls it a saddle, the fact that there may be saddles somewhere in the vicinity does not excuse his error.
You simply don't know how
colossally wrong you guys are. You seem to think you can continue to bluff your way through this discussion, but your original error was so blatanly uninformed that this is just not an option. You seem to think your critics are just as uninformed as you are, or at best only marginally more informed. That is not the case, and you are visibly unable to keep up with this discussion.
As a result, a single page of the PDF file can contain different layers with different content."
The referenced help page is for printing PDF complex PDF files. The Obama PDF is not a complex file. It's a straightforward flat file containing a couple dozen ordinary objects in a well-supported standard hierarchy of groups -- i.e., for associating content with its clipping masks. Adobe publishes this help file precisely because not all PDF producers or PDF renderers have been written to properly express non-standard object hierarchies, such as those InDesign can be coerced to produce. Your help file refers to a very rare corner case, not the expected case.
This is why it was important for you to answer the question regarding PDF and PS as interpreted programming languages; the richness of expression they embody sidesteps your straw-man objections.
The help file instructs me that when I'm faced with such a complex file, I can "flatten" it within Adobe Acrobat Professional. When I open the Obama PDF in Acrobat Pro 9, guess how many layers I see?
No, not one.
Zero. That's right, the Obama PDF contains
absolutely no information that Acrobat recognizes as layered content. I opened an InDesign document -- a DVD label I designed -- that contained three layers, two of which were visible. I exported that as a PDF with the layer-export option turned on, and then opened it again in Acrobat Pro.
Zero layered content. Why? Because InDesign knows that PDF 1.3 cannot support it.
In fact, the only way I can add layered content to a PDF is by importing another document as a "layer" in Acrobat and then saving it with PDF 1.6 compatibility. The resulting document lists "Jay's New Layer" only as another object on the page. Other PDF tools and renderers cannot interpret the meta-information that Acrobat uses to recognize layered content it has added. That's because, as I said, the PDF data structures cannot represent layered content directly. Hence Adobe publishes instructions for flattening such data using Adobe products so that other renderers reproduce it correctly.
Sorry, frantic Googling for keywords is not a substitute for correct understanding and practical experience.
