Northrop Grumman root certificate not trusted?

I'm running Acrobat XI (11.0.14) on Mac OS X 10.11.3

I received a digitally signed document from a trusted source at Northrop Grumman.  The digital signature isn't trusted.  I right-clicked on the signature and reviewed the trust train: Northrop Grumman Corporate Root CA-G2 > Northrop Grumman Corporate Signing CA-G2 > Individual's Digital Signature

Both the Northrop Grumman Corporate Root CA-G2 and the Northrop Grumman Corporate Signing CA-G2 aren't trusted.  Shouldn't these be trusted by default.  Isn't Acrobat XI pre-loaded with major trusted root certificates?  Isn't OS X also similarly pre-loaded?

I know I can trust this individual's signature directly from the document, but I'd prefer not to.

Any ideas?