ABA says document metadata is fair game
The ABA’s Standing Committee on Ethics and Professional Responsibility recently ruled that lawyers who receive electronic documents could look for and use the hidden metadata information wired into the document even if the communication in question was provided by an opposing attorney. For more information see this ABA announcsement … [more].
pm blog 
This should “open” some eyes too the usage of .pdf for coorespondence vs the standard practice of .doc files. Metadata puts everyone at risk, it has been proven time and again. .pdf is the most secure way of eliminating this protential nightmare.