Learn Swedish: Jag vet att filen inte är farlig. - I know that the file is not dangerous.

Because the second part of the sentence (att filen inte är farlig) is a subordinate clause. In Swedish, subordinate clauses follow the BIFF rule: Bisats (subordinate clause), Inte, Före (before), Finita verbet (the conjugated verb). This means sentence adverbs like inte must go before the verb, rather than after it like they do in a main clause.

How would the word order change if I just wanted to say "The file is not dangerous" as its own sentence?

As a standalone main clause, the verb must come in the second position and inte comes after it: Filen är inte farlig. This perfectly shows how the BIFF rule changes the word order when you connect the thought with att!

How can I tell from this sentence whether a file is an en-word or an ett-word?

There are two clues here that it is an en-word (en fil). First, the definite form (the file) is filen, ending in -en. Second, the adjective farlig (dangerous) stays in its base form. If it were describing an ett-word, it would need an extra -t at the end (farligt).

Is the word att pronounced exactly how it is spelled here?