Documents are literal in this case.

It's legitimate business deals.

Blackmail would be illegitimate business deals.

But being legitimate doesn't mean public. They're private documents, for private companies, doing private business deals.

But, they create a path -- a connection. They're a path through the woods completely surrounded by scat (evidence).

It's like finding out Prime Minister Abe from Japan had a Vatican Bank account.

Nothing is illegal about that, but just knowing he was dealing with the Vatican directly opens up an entirely new avenue for investigation.