I guess, but 'add7' chords do not exist.. there is no need for them. Any triad with the seventh added becomes a seventh chord of some description. The purpose of the 'add9' suffix is more to distinguish it from a ninth chord... for example:

A Cadd9 is a C major triad (C, E and G) with the ninth (D) added.

A Cmaj9 chord includes the 7th, so you'd have C, E, G, B and D

It's an 'add9' because the note you're adding is in the second octave, so it is the ninth note of the parent major scale. Play a 2 octave major scale... the ninth note you play is the one you want for the add9.