-- or in English: the Vienna Codex, Austrian National Library, Latin manuscript #15. (Or in German: Die Wiener-Kodex, Österreichische Nationalbibliothek, lateinische Handschrift Nummer 15.) It's the single known source for books 41-45 of Livy. It was written in the 5th century. Notes at the end of the text let us deduce that originally the volume contained books 41-50, and that by the late 8th century it had somehow been split in half, and that this half, books 41-45, had come into the possession of Theodard, who as we know from other sources was the Bishop of Utrecht from 781 to 790. Or possibly Thiatbrat, who worked at the monastery of Utrecht under Theodard, but in all likelyhood it belonged to Theodard. Notes written in the margins in handwriting characteristic of Anglo-Saxon England indicate that the manuscript may have come to Utrecht from England, perhaps one of the books brought to the continent by the famous English scholar Alcuin, when Charlemagne invited him to Aachen help start the Carolingian Rennaissance. Utrecht may very well have been on Alcuin's way to Aachen. If a bigshot like Alcuin were passing through Utrecht it wouldn't have been unusual for him to meet the local bigshot, Bishop Theodard, and for the two of them to have exchanged gifts, such as books. John Brisco, in his 1986 edition of books 41-45, mentions that the 19th-century scholar Michael Gitlbauer brought up the possibility that Alcuin gave the book to Theodard, and that he, Briscoe, also thinks it could have been that way. Gitlbauer and Briscoe are bigshots in Classical Studies, and Briscoe, especially, in not given to wild irresponsible speculation, so if he thinks it's possible, then, well, I've got to consider it as a possibility.
Was it Alcuin who separated the the original volume containing books 41-50 in half, giving the first half to Theodard and taking the other half, books 46-50, with him on to Aachen? Everyone agrees that Codex Vindobonensis Bibl Nat Lat 15 is a particularly bad copy, badly made, full of copying mistakes, the work of a less-than-world-class scribe. Alcuin was a world-class scholar. Did he have another copies of books 41-45, which he preferred to keep as his own?
Nobody knows. As far as I know, nobody has been able to make so much as a responsible guess. And of course, everything in the previous paragraph assumes that Alcuin gave Codex Vindobonensis Bibl Nat Lat 15 to Theodard, which we shouldn't assume. It's a possibility, not a certainty. Also, nobody knows what happened to Codex Vindobonensis Bibl Nat Lat 15 between the 780's and the 1520's, when it was found on a shelf in a monastery in Switzerland. A few years after that it was printed, and many, many editions have been printed since.