Learn Finnish: Laiton kirja takavarikoidaan aina. - An illegal book is always confiscated.

This happens because of the passive object rule. When the verb is in the passive voice, like takavarikoidaan, a total object that would normally take the -n ending drops it. This leaves the object looking exactly like the basic nominative form.

How would laiton kirja change if the sentence had a specific subject doing the confiscating?

If someone specific was doing the action, the object would take the normal -n accusative ending. For example, 'The police confiscates an illegal book' would be Poliisi takavarikoi laittoman kirjan. The dropped ending is a special rule for passive sentences and commands.

Does the passive object case drop rule still apply if we make the sentence negative?

No, it does not. If the sentence becomes negative, the object must switch to the partitive case, just like in regular active sentences. 'An illegal book is not confiscated' would be Laitonta kirjaa ei takavarikoida.

What type of verb is takavarikoida and how is this passive form made?

The base verb is takavarikoida (to confiscate), which is a type 2 verb. To form the passive present for type 2 verbs, you just take the basic infinitive and add the passive ending -an or -än. This gives us takavarikoidaan.