Specifically the conspiracy theory is that Trump fired Comey because he wanted to stop the "Russia/DNC hack" investigation. There is absolutely nothing in this leaked doc that says that this was the reason for Comey's firing, nor has Trump ever said that this was the reason, nor is there any other evidence for this theory. However the Trump derangement syndrome people are so desperate for validation of their conspiracy theories that they jump all over docs like this and imagine they say things that they don't.
Likewise, you are so desperate to find justifications for everything Trump does, that you consume the first excuse you see on Breitbart or fringe YouTube videos, no matter how weak its standing or logic is.