Nasa Archives on Planet X

I found some NASA files about various things including Planet X pretty secret.

adsbit.harvard.edu...

I like the fact that they know it's out there, but they cannot pin-point its exact location. If they do actually find it, does anyone think that they'll share the info with us? I always think that given the Summerian stories of planet x, it would put the finding of the planet high up there with the existence of extraterrestrial life that's currently visiting the earth, thus it would be kept very secretive.

It starts out by saying "Planet X, if it exists at all..." Most astronomers still don't take Planet X seriously do they? Where's the proof?