There is a good chance the documents are covertly marked as
you suggest, the ostentatious classification markings a ruse for
untutored yokels to fancy are genuine.

Covert markings have been in use for a long time, as well as
ostentatious markings. On paper as well as digital and other
forms of electronic.

And certainly packets carry unique markings in a variety of
overt and covert types.

Some of the techniques fall under the inadvertent emanations
rubric associated with Tempest -- which has blossomed well
beyond the FOIA releases from the late 1990s. TSCM is a
marvel of duplicity and ruse.

At 08:16 PM 5/13/2014, you wrote:

From: Black Fox <fox@vbfox.net>
On Tue, May 13, 2014 at 2:58 PM, coderman <coderman@gmail.com> wrote:
> On Tue, May 13, 2014 at 1:00 AM, John Young <jya@pipeline.com> wrote:
>> > We've seen the Greenwald book No Place to Hide, where are the
>> > promised gush of Snowden documents available? His publisher
>> > doesn't show a source. Surely not another marketing tease.
>> great question; let us know if you find them!
> http://glenngreenwald.net/pdf/NoPlaceToHide-Documents-Compressed.pdf

If I were the telephone company from which the records were requested, I'd note that the records were requested in "electronic" format. Then, I'd ask a programmer to write a program to write a program to generate pdf files with embedded "captcha"-type text: Images that are quite apparent to the human eye, but are very difficult for any computer to make any sense of. All the phone records would be there (in no particular order), and they'd all be very readable to humans, but...
Jim Bell