Jude quoted Enoch
Jude clearly quoted from or paraphrased a version of the Book of Enoch, not the other way around. The Yale Library states:
The Book of Enoch, written during the second century B.C.E., is one of
the most important non-canonical pseudepigraphical works.
While it is likely that the current version includes later additions, it is hard to imagine that Jude's lines, avowedly quoting Enoch, would be one of these. Using Occam's Razor leads to the conclusion that Jude is quoting Enoch, not the other way around.
Jude also summarized Enoch's teaching
Not only did Jude quote from the Book of Enoch, he also summarized part of the book earlier in his letter when he said:
He has kept, with eternal chains in darkness for the judgment of the
great day, the angels who did not keep their own position but deserted
their proper dwelling. In the same way, Sodom and Gomorrah and the
cities around them committed sexual immorality and practiced
perversions, just as angels did, and serve as an example by
undergoing the punishment of eternal fire. (1:6-7)
This description almost certainly derives from Enoch's first chapters, known as the Book of the Watchers:
Enoch, thou scribe of righteousness, go, declare to the Watchers of
the heaven who have left the high heaven, the holy eternal place, and
have defiled themselves with women, and have done as the children of
earth do, and have taken unto themselves wives: "Ye have wrought
great destruction on the earth: And ye shall have no peace nor
forgiveness of sin." (Enoch 1:12)
Inspired?
We can deduce from the above that Jude regarded the Book of Enoch as an authentic source describing the course of the fallen angels mentioned in Gen. 6. Those who believe that Jude was inspired by the Holy Spirit will admit that at least this much of the Book of Enoch is also inspired. Whether Jude regarded the entire book as scripture is debatable. We are probably well served to regard it, as the Jewish Encyclopedia does, as
... one of the most important pieces of apocalyptic literature; it
furnishes extensive contributions to our knowledge of Jewish folklore
in the last pre-Christian centuries; it shows apocalyptic literature
in its beginnings, and above all it is a source of information upon
the religious ideas of Judaism, especially concerning the Messiah...