A PDF was automatically downloaded while my phone was turned off

So, I live in a city in Brazil called Curitiba (this will be important to know) My phone was turned off, and then after it was charging for a while, I came across a PDF that had downloaded itself onto my phone. Its name was "Long live Curitiba 2024" It was over 100 pages long and was just detailing the benefits of the city. But I'm extremely worried because I've never been on the city's website and I've never downloaded any PDFs on my phone. How did this get there? This file appeared out of nowhere while the phone was turned off, I ran Avast and it didn't detect anything