And good news: it's been open sourced: https://freecomputerbooks.com/Expert-C-Programming-Deep-C-Se... and its well regarded on Hacker News https://hackernewsbooks.com/book/expert-c-programming-deep-c... .
There are several links to PDF versions of the book. None of them include either a copyright page or a statement that it's been released as open source.
The author's own website <https://afu.com/> includes errata for the book, but doesn't provide or mention a free copy.
A free sample of the Kindle version of the book does include a copyright notice. A book published in 1994 is not public domain unless it's been explicitly released.
Something that appears to be a legitimate PDF sample (not the while book) is here:
https://ptgmedia.pearsoncmg.com/images/9780131774292/samplep...