If I wanted to pass the content of a file to an AppleScript in Hazel, I’d probably do it like this, defining a function for calling the AppleScript within a shell script that reads in the file content to a variable I can then just pass in.
You could also read the content from the file directly in AppleScript. theFile is the object you would reference. I just personally find shell scripting is often more straight forward than AppleScripting.
Note, if the OP does happen to have Keyboard Maestro (all Mac automators should ), they would also have to leave their Mac unlocked to get this sort of interaction to work, which is bad practice from a security standpoint.