Understanding Prior Restraints and NDA's

Under the First Amendment we are all protected from restrictions on our writing, reporting, and anything we release to the public or press.  However, many companies, corporations, and private institutions require employees to sign a Non-Disclosure Agreement, or NDA.  It is understandable that these would be required since it prevents sensitive material from being leaked.  Although we are protected from prior restraints by the First Amendment, it is applicable only to public actors.  This means that the Government cannot restrict your First Amendment rights in any way.  Private actors have no such restrictions.  For instance: if a private university were to impose a NDA and a professor disclosed a sensitive piece of information to the public, the university would be able to fire said professor without being sued for a First Amendment violation.  An article that does a good job explaining some of the rights protected by the First Amendment can be found here.  In summary, the American people are protected from restrictions imposed by the Government, not from private institutions, as per the intentions of the Founding Fathers.