Learn Portuguese (Portugal): O seu livro está aqui.

No. Even though the direct object pronoun for 'him' or 'it' is also o, in this sentence O is simply the word for 'the'. It goes with seu livro to mean 'the your book'. In Portuguese, we usually put a 'the' (o or a) before possessives like seu.

Why do we say O seu livro ('The your book') instead of just Seu livro?

In European Portuguese, it is standard to use a definite article (o, a, os, as) before a possessive word. Since livro (book) is a masculine word, we use the masculine article o.

Does seu always mean 'your'?

Not always! Seu can mean 'your' (when speaking formally to someone using você), but it can also mean 'his', 'her', or 'their'. We know it means 'your' here from the context of the translation. Notice that seu matches the masculine, singular word livro, not the gender of the person who owns it.

Why do we use está instead of é for 'is'?