In this case, the TSO's were not on a fishing expedition for non-travel-related contraband, but they were doing an "investigation" into something that could, possibly implicate airport security. I'm not saying that I agree that going through papers one considers "suspicious" is part of a proper WEI search, but a good test case, this is not.
Wrong.
The minute they started reading the document was the moment they stepped over the line. A document cannot be travel-related contraband.
I would submit that this is a perfect test cast as the victim of the intrusive TSA search is a writer with an unpublished manuscript. It's really no different than the TSA reading written materials that I might have that are considered company confidential.