https://libgen.gs/

Z-Library is still accessible on the Onion Network:

http://bookszlibb74ugqojhzhg2a63w5i2atv5bqarulgczawnbmsb6s6qead.onion/

If you weren’t aware already, use the Tor browser to access the website.

PDF DRIVE:

https://www.pdfdrive.com/

I'd recommend uploading any PDFs you download from z-library and the above site to VIRUS TOTAL:

https://www.virustotal.com/gui/

"free ebooks" are notorious for viruses like RAT.

Stay safe.

If you wish to convert PDFs to EPUB, there is a great bot on Telegram: https://t.me/newfileconverterbot