I created a file in Illustrator CS6 (v. 16.0.0), and saved it as an (editable) PDF. When I try to reopen that same PDF inside Illustrator CS6, however, I get a "Could Not Open The File" error.
The file opens in Acrobat just fine, but I need to continue editing/working on it. Opening it in 5.1 works but it's all flat and not ideal for editing. Renaming the extension to .eps or .ai didn't work, either. I also looked into potential font conflicts (none) and restarted my Mac (OS 10.7.5) to no avail.
Thoughts/suggestions most welcome!
Illustrator is not designed to be a pdf editor, so save a .ai file backup always.