Leaving aside sophisticated theology for a moment, quite simply, Catholics pray as Christ instructed. Just look in the Bible.
During the Mass:
Priest says: "Let us pray in the words our Saviour taught us." (Or similar phrasing).
Then priest and people TOGETHER say the "Our Father" (just as Jesus taught the disciples, straight from scripture).
Then priest says: "Deliver us Lord from every evil and grant us peace in our day. In your mercy protect us from all anxiety, as we wait in joyful hope for the coming of our Saviour." (approximately)
Then the congregation (only) says "For Thine is the kingdom, etc...." It is a separate prayer.
Here's a somewhat unrelated but true story:
My mother went to grade school in Chicago in the 40's. Apparently in those days, class began not only with the Pledge of Allegiance, but the Our Father as well. Yes, this was a public school.
Before her first day, my Grandmother, a devout Catholic, told my Mom, "Now they are going to say the Our Father at the beginning of school, BUT, they are saying the Protestant version! So after you say "deliver us from evil," you stop! Stay silent for the rest of it!"
So God was then allowed in the classroom, but only the socially dominant WASP version.
In your mercy keep us free from sin and protect us from all anxiety, as we wait in joyful hope for the coming of our Saviour Jesus Christ.
So Matthew 6 verse 13 is only in the Protestant Bible?