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It has a great offer exchanging BTC for PAX, but I don't know if I can trust them. Thanks for your answer.

Take a look here. https://coinmarketcap.com/currencies/paxos-standard/markets/
Most PAX trading volume comes from BitZ. You can also trade it on Binance. I would suggest you don't send any money to an exchange you don't feel comfortable with.

Thanks

Whois records show that the site started its operations in November 2019. They are brand new in this game.