You could say "I've attached a word file" and it will sound natural. You can use the verb "attach" when you want to say that you are connecting two objects.

"File" is generally okay for any type of attachment, but it can't hurt to be more specific. You could say: "I have attached a Word file to this email". More common in English is to say "Word doc", which is short for "document", but file is also a good, formal choice.