Is the catechism of the Catholic Church seen as official doctrine for Catholics? Or is it seen as something that can be challenged or even, in parts, refused?
Pope John Paul II wrote, in the Apostolic Constitution promulgating the Catechism in 1992,

The Catechism of the Catholic Church, which I approved 25 June last and the publication of which I today order by virtue of my Apostolic Authority, is a statement of the Church's faith and of Catholic doctrine, attested to or illumined by Sacred Scripture, Apostolic Tradition and the Church's Magisterium. I declare it to be a valid and legitimate instrument for ecclesial communion and a sure norm for teaching the faith.
This catechism is given to [the Church's Pastors and the Christian faithful] that it may be a sure and authentic reference text for teaching Catholic doctrine and particularly for preparing local catechisms. It is also offered to all the faithful who wish to deepen their knowledge of the unfathomable riches of salvation (cf. Jn 8:32). It is meant to support ecumenical efforts that are moved by the holy desire for the unity of all Christians, showing carefully the content and wondrous harmony of the Catholic faith. The Catechism of the Catholic Church, lastly, is offered to every individual who asks us to give an account of the hope that is in us (cf. 1 Pt 3:15) and who wants to know what the Catholic Church believes.

The Catechism is a sure norm for teaching the faith: it is a sure and authentic reference text for teaching Catholic doctrine. Thus it is official doctrine, inasmuch as it records what the Church teaches. That is, the Catechism puts forth what the doctrine is; it is not actually doctrine itself.
However, because it represents the teaching of the Church's faith, it is not something to be challenged by Catholics. It is an authentic statement of the teaching of the Church.
All of this is what is meant by &quot;preparing local catechisms&quot;: the different Bishops' Conferences [which are generally arranged on a national basis] can prepare their own translation of the Latin original; YouCat, the Youth Catechism, has also been published. There are non-English translations too. Provided that these local versions — each prepared for particular circumstances — also represent the teaching, they do not challenge the Catechism. The Catechism is an authentic statement; it's not the authentic statement. But because it is an authentic statement of Catholic doctrine, it's a useful tool for stating what that doctrine is, and for comparing other teachings to see whether they are consistent with Catholic doctrine.
I am sure there are parts which non-Catholics might take issue with; and by the same token there will be parts which they might be surprised to find it does in fact contain.