On behalf of Adobe ...
Adobe Illustrator is not, repeat is not, repeat yet again is not a general purpose PDF editor!!!!!
(To be honest, I do understand why some people think to the contrary. Some very misguided Adobe marketing folks over ten years ago wrongly trumpeted the alleged "fact" that PDF was Adobe Illustrator's native file format. In fact it isn't and never was. Illustrator's native file format is buried as private data inside what looks like a PDF file!!!)
The only PDF files that Adobe Illustrator can safely edit are PDF files that are created by the save as PDF feature of a version of Adobe Illustrator equal or less than the version you are editing with and the "preserve Illustrator Editing Capabilities" option was checked when the PDF file was created. When such PDF files are created, two copies of the content are put into the PDF file - the first copy is PDF content and the second content is "private Illustrator data" which represents the content as processed in Illustrator including layer information, swatches, group information, etc. When you open a PDF file in Adobe Illustrator, an attempt is made to find that private Illustrator data. That is what is safely opened in Illustrator. If that private Illustrator data does not exist, Adobe Illustrator attempts to interpret the PDF data and convert it into equivalent Illustrator objects. Not all PDF objects are part of the Illustrator imaging model and there are some incompatibilities. For example, with the exception of linked placed objects, every graphical object in a PDF file must be in the same color space. Thus, if your non-Illustrator PDF file has multiple color spaces, it will converted to only one color space. Folks, that is a very lossy operation! Likewise, character encodings may change and may be corrupted. And some objects in your non-Illustrator PDF may be significantly modified in ways you may not find acceptable and/or discarded.
Bottom line ... in an emergency, use of Illustrator to modify or extract PDF content may work, but it is definitely not something that is valid use in a generalized PDF print publishing workflow for examining or otherwise editing a PDF file. And if you ignore this advise, you will get what you justly deserve.
- Dov
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