Why is it shorter than the other versions?
The Catholic version of the "Our Father" prayer does not contain the "Doxology". There are good biblical reasons for the omission of this doxology from New English and other popular versions of the prayer:-
"For the kingdom,
the power and the glory are yours.
Now and for ever. Amen" (New English Version)
Common bible versions, such as the New International Version, and the Contemporary English Version, exclude the doxology from the Lord's Prayer in the main body of the text (in Matthew 6:9-13), and instead feature it as a footnote on the page. Critical editions of the New Testament used by the United Bible Societies (an organisation representing 145 national bible societies) concur that this doxology does not belong to the original manuscripts of Matthew's gospel, and seems to have been added at a later date.
In 1963, the Second Vatican Council decreed a revision of the liturgy (undertaken by the ICEL, International Commission on English in the Liturgy). In 1969, the doxology was added to the Catholic Mass, not as part of the "Our Father", but following shortly afterwards. In the Mass, the Lord's Prayer is spoken together, followed by the Priest praying:
"Deliver us, Lord, from every evil, and grant us peace in our day. 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 Savior, Jesus Christ."
and then the doxology ("For the kingdom, the power, and the glory are yours, now and forever") is prayed by the congregation.
This section of the mass falls just before the sharing of the peace, where the priest wishes the congregation the peace of Christ with the words "The peace of the Lord be with you always" and all who are present share God's peace by shaking hands or embracing each other (depending on the customs of the church).