I have some problems with my party on that topic so I would like to read your opinions on that matter.
As far as I know, the majority of the Imperium does not know anything about the Demons and most Xenos except from scary stories. On the other side I read some books where better situated commoners know at least a little about them...
And the most importent thing is, how much do fresh acolytes know? (If the Inquisitor lets them find out for themselves
)
Example: My Acolytes are in warptransit, there is an engine failure and the guardsman starts running around to search for demons... which in my opinion would not happen, especially if the captain said (not very convincing though) that everything is fine