The Armenian Rite is one of around 21 of the Eastern Catholic Rites. All of these Rites are various expressions of Catholicism as expressed by the various Eastern Catholic Churches. All of these - Maronite, Byzantine, Coptic, Chaldean, Armenian, etc - are in full union with the Pope and, thus, fully Catholic. The Liturgies, however, look different from a Latin Rite Mass. The Armenian Catholics are found primarily in the Middle East, though there is an Armenian Rite parish in Pennsylvania (maybe others in the US, too). Any Catholic can fulfill the Sunday obligation at any Catholic parish of any Rite; however, it is encouraged for Eastern Catholics to attend Eastern churches so as to sustain the traditions and practices of these smaller Churches throughout the world. I am not familiar with the specific differences of the Armenians vs Roman Catholics.