Gostaria de saber se posso usar a fonte gratuitamente em uma marca que irei registrar no INPI?

If the font is public domain then you can use it for free.

if the font is open source< free for personal use< read the documentation that comes along with the font> if there is no documentation<< send the font author?designer a private message here at dafont and directlY ask the author for the terms for commercial use. You can also send him/hjer an email if that is available.