到 dou2 is a word with different meanings. It means “to arrive” 到 dou3 in 3rd tone but in some situations we use it as an auxiliary word. In certain contexts, we will use the word 到 dou2 after the verb and before the object.
I saw ngo5 tai2 dou2 我睇到
I saw you ngo5 gin3 dou2 nei5 我見到你
I heard ngo5 ting3 dou2 我聽到