Not Action in Alfred, but Universal Action. You use it as the trigger, not as the result.
To the conversation above, the Is File? Automation Task is not meant to check if a random string is a file, it checks if an existing path is a file as opposed to a folder. To check if a given path exists you could use the File Conditional. But Universal Actions, as per @Stephen_C’s suggestion, are what I’d recommend too. That way you don’t have to worry about checking what the type is, Alfred does it for you.