here's what I know so far: The book comes from Bohemia (now Czech Republic) in the medieval period, it was written by monks. it is the largest medieval manuscript in the world
Legend has it that a monk was about to be immured for breaking monastic vows but promised that if they let him go he would write a manuscript containing all human knowledge (at least for the time, anyway) He doubted he could accomplish the task so he prayed to Lucifer, he offered Lucifer his soul if Lucifer helped him complete the manuscript. A picture of Lucifer is on one of the pages and is the earliest known picture of a demon (at least in Christianity). Obviously nobody knows whether he made the deal with Lucifer or not because nobody knows whether Lucifer exists or not, but it is estimated that the book would take 5 years of nonstop writing with just one scribe.
I know that the Codex contains a version of the Latin Bible but it does not include the books Acts or Revelations. There were many illustrations in gold,red,blue,yellow and green. the most famous part of the book is the picture of the devil which created the modern image of satan (even thought he picture was of Lucifer the prince of Pride while Satan is the Prince of Wrath)
Aside from this, what was in the manuscript? this only covered half of the document. So what other information was in the book?
And please don't make this into a debate of wether on not god is real. I honestly don't care whether or not God is real and it is unrelated to this question.
I've seen this question asked before; as a rule if you want to find out what is in a historical manuscript you would want to consult the catalog or website of the institution holding it(in this case the National Library of Sweden in Stockholm). If we check the catalog, we find a listing of the book's contents as follows: A Latin translation of the Hebrew Bible plus apocrypha, Flavius Josephus's Antiquities of the Jews, the Etymologies of Isidore of Seville(a very popular encyclopedic medieval reference work), a series of medical texts grouped under the rubric Ars Medicinae, a New Testament(note that the order is somewhat off and Acts is at least according to the catalog included along with the Apocalypse of John but in the Old Latin texts), a confession of sins, a set of conjurations, a chronicle of Bohemian history, and a list of people attached the monastery at which it was written as well as a calendar of feasts. All of these are relatively typical medieval texts that would not be very surprising to find circulating in a monastic context. Incidentally the website of the National Library has a series of nice articles, one of which explains the origin of the legend; it seems that someone had seen a note listing the author as a recluse or confined, meaning that he was living alone within the monastery-in English, what would be called an anchorite-and thought it meant he had been immured or sealed up.
One last note: The portrait in the Codex is not the earliest known picture of a demon in the west; demons are abundant in Romanesque art(especially Last Judgements, for instance the Last Judgement tympanum at Autun Cathedral), and documented as well in Anglo-Saxon art.