score:6
CPF is used for tax-related purposes, quoting Wikipedia:
CPF is the Brazilian individual taxpayer registry identification, a number attributed by the Brazilian Federal Revenue to both Brazilians and resident aliens who pay taxes or take part, directly or indirectly, in activities that provide revenue for any of the dozens of different types of taxes existing in Brazil.
Since you're not a Brazilian resident it's not really relevant, if you need it just for this one transaction you may use an on-line generator to generate a fake but valid one. I did it several times when buying stuff through Brazilian websites and applying for jobs there, they often assume that everyone has a CPF number so this field is mandatory on many websites.
It's also possible to get one through a Brazilian consulate, but in your case it'd be overkill.