I agree with Crazydre that it won’t be a problem when going to Argentinian side of Iguazu (just don’t exit the bus, I did that last week and no one cared).
But later, when you’ll be leaving Brazil by any other border (I’m assuming your passport is not Brazilian), you need to have stamped Cartão de Entrada e Saída (Entry / Exit card), not having it may be a big issue with Policia Federal, which are rather infamous for their bureaucracy and being petty.
Just to be safe (although I may be a bit paranoid, I had some issues with PF), I’d recommend:
Otherwise you should be good but may have problems in the future, from my experience it depends on mood of the officials.
It’s the same there – since MERCOSUR citizens and residents, i.e. the vast majority of people crossing, do not even need passports to cross, having fixed border control is deemed to be superfluous.
Thus, those who are neither MERCOSUR citizens nor residents have to self-report to immigration authorities when entering/exiting.
When you get to the Argentinian side of the border, locate the immigration office and obtain an entry stamp. The fact that you have no Paraguayan exit stamp or any Brazilian stamps should not be an issue, as they are not relevant to your conditions for entering and staying in Argentina
Credit:stackoverflow.com‘