From this one quote you can't interpret that Jude is quoting from The Book of the Secrets of Enoch. It could well be just Oral Tradition. It could be from the mysterious Q, or L, or M documents, we don't know. Paul even quotes a Greek prophet, not necessarily implying that the Greek is inspired.
Very astute and, except for the alleged existence of Q etc, positively correct. The fascination with pseudepigrapha among those who also consider themselves learned is difficult to explain indeed. One one hand we are warned against "literal" interpretation of biblical ancient literature and, on the other, we are expected to take Enoch seriously--- as if ancient literature were a buffet where each person decides what is true and what is not. That is postmodernism at its worst.
Yes, Jude may not have quoted Enoch directly. As you pointed out it may have been a source common to both books or it may have been tradition. Regardless, quotation in a canonical book does not mean the source quoted is inspired. And certainly there is no one on this thread-- especially not a scoffer-- who is qualified to modify the Canon.
Jude 1:14 And Enoch also, the seventh from Adam,
BTW, Mark, this quotation makes it clear that generations were not skipped in Genesis as young-earth critics have suggested.