It's a matter of jurisdiction. The current identification most people carry (Carteira de Identidade, CI) is issued by the state-level Publicy Security Office. Two things here prevent using this data for voting: first, the data collected for issuing these ids are technically property of the PSO, and can only be used for forensic reasons. Second, this is state-level, while elections are organized at a federal level.
The federal government is starting to introduce a new document, the Documento de Identidade, DI. This will actually be the first federal level identification document in Brazil, and should replace all other documents people carry right now (state-issued id, voters id, cpf). This is currently in trial in a few states, and it will be at least 10 years or so before people are required to carry them, however.