Hi,
I picked this game up a few months ago, and have been more or less bumbling through the setting as best I can. As a preface, this is the first time I've done anything with the 40k universe, the extent of my familiarity being that I know there's a miniatures game. As such, I've been largely relying on wiki entries, fluff from the books, and HP Lovecraft to reference anything that I throw into my campaigns. If it's not quite cannon, I don't particularly care as long as it's close enough.
The latest leg of my adventure will see the characters tracking down a renegade psycher who has far too much information on the Black Ships nature and wants to establish a haven where his evolved kind can remain in peace. He's been foiled in the past, and has decided to build up his influence from the ground up by heading to a feudal world.
Now this is where my understanding falls flat about the universe. This, so far, is what I believe to be true of feudal worlds: these worlds are primitive societies where the vast majority of people know nothing about the true Imperium. This could either be by design of the leaders in aeons past, or by circumstance removing their ability to contact the greater universe. Space travel, modern weaponry, and mechanical devices would seem like magic, and any "proof" to the contrary would be in archaic writings from thousands of years ago that would seem like a strange myth from a dead civilization. The leaders of these worlds would likely know more about the Imperium, as they might pay taxes in manpower and psychers to the mysterious beings who appear every generation or so. Whether the leaders know anything beyond this is up in the air, and largely immaterial. They could well think that the tax collectors are gods who must be appeased. The Imperial Cult would again likely exist due to the influence of the Ecclisarchy, but again, it would likely take a unique shape due to the remoteness of direct teaching from the clerics and the amount of time that has passed.
Now the question is, how far off the mark am I here? I understand that in a sense it's accurate, as with a million planets surely one resembles this model. But is this the norm for a feudal world? If not, how are they normally run? The reason I'm asking is that if so, these planets would seem ripe for heretics to gain a foothold by slipping under the radar of the the Inquisition and Ecclesiarchy. Another question is if such a world existed, would there be a "prime directive" so to speak which would limit the players from bringing their futuristic weaponry into such a society?