If you must own the PDF outright, RedShelf or VitalSource sometimes sell e-textbooks of the reprint editions. Expect to pay ~$35 per volume. For the serious scholar building a digital library, this is the cleanest route (no blurry scans).
You can find René Wellek A History of Modern Criticism: 1750–1950 available for digital reading and borrowing on Internet Archive a history of modern criticism rene wellek pdf
In the sprawling landscape of literary theory, few works command the same reverence and scholarly weight as René Wellek’s monumental series, A History of Modern Criticism: 1750–1950 . For graduate students, comparative literature scholars, and intellectual historians, Wellek’s eight-volume magnum opus remains the definitive roadmap of how Western thought learned to read, judge, and interpret texts. If you must own the PDF outright, RedShelf