https://b-ok.cc/ Seems to work pretty well for me. There’s a lot not on there, but it’s a good place to start.

Libgen

Libgen, as others have said. Although I find it to be better with STEM shit and less good with history texts or whatever.

Occasionally 4shared might have something libgen doesn’t but it’s very rare.

You might also luck out searching for “[book title] blogspot pdf”, maybe sub out blogspot with mediafire or whatever file hosting sites you’ve seen used in the past. Sadly google is probably the best search engine to use. And a lot of the hits are like 3 page PDFs directing you to other links, those are all scams, don’t click anything inside those PDFs.

Finally, since I mostly needed a ton of math books, I have a Russian site on an old computer I could dig up (anyone hit me up if you’re interested in this). But it’s mostly grad-level texts and genre classics, not calc 1 texts (and just a giant index, not searchable like libgen afaik).