CC on a Mac.
I have 100+ page document in InDesign. I'm illustrating it by creating the artwork in Illustrator and placing the artboards into InDesign. As of about an hour ago I am unable to place or update or relink to one particular Illustrator file. Whatever I try, I get an InDesign error saying "Unable to open PDF file". I've trashed my preferences, rebooted, and even made a copy of the Illustrator file and tried to relink to it. Same error message. I am able to open and work with the Illustrator file in Illustrator; I am able to work normally with other Illustrator files from within this InDesign document.
PS: I created a new InDesign document; it, too, refuses to work with this particular Illustrator file and its copy.
Sounds like the Illustrator file is damaged.
As Peter suggests, the Illustrator file sounds like it is damaged.
Open the illustrator file in Illustrator, and resave it to a different file name.
Try the new file.
I believe she already tried making a copy of the file in Illustrator. I think it may need to be rebuilt from scratch, or try an old copy if there's a backup someplace.
I don't know how the copy was made. If it was just copied on the desktop ... the way I suggest would be to open the Illustrator file and save it to a new file.
Even if it means copying the artwork to a completely new file.
Thanks all. In the end I was forced to recreate the Illustrator file.