What PDFs carry without telling you
Author is the big one — it is usually taken from the account name on the machine that produced the file, so a document exported from a home computer can carry a full personal name into a professional context.
Producer and Creator name the software and often its version, which says something about your setup. Creation and modification timestamps say when you worked on it, which can be more revealing than it sounds: a document dated the day before it was supposedly written is a detail people have been caught by.
Title is sometimes the original filename, which can be an internal reference or an earlier draft name you would not choose to publish.