I recently moved my some keynote documents into backup HD. And I found I can't open some of those someday. It showed that "xxx.key can't be opened",and then I just try open it in PDF preview, it showed that "It may be damaged or use a file format that Preview doesn’t recognize."
But something weird was that those fail-to-open files remained normal size. Right now I'm not sure whether it is error of writing files in HD or keynote software itself.
Any other ideas as to how these documents can be repaired?