You sbsolutely do have a right topost blassified documents if you come across them, but have not attained a security clearance.
There's definitely a massive "should" aspect there, however, the courts will protect you in that case. The one who got them for you, or if you committed a crime in acquiring them however...
Oddly, classified documents that could theoretically harm real people are legal to share with others but don’t you dare try to share the latest Beyonce track or there will be hell to pay.
Perhaps the RIAA should be in charge of national security from now on?