The user wants PDFs and EPUBs, so they're probably looking for a way to legally access his books. I should check if his works are available in Serbian or other languages. Maybe some of his books are translated, but the user might need to download them. But I have to be careful here because promoting piracy sites or enabling illegal downloads is against policy.
Another angle is using library databases or services like OverDrive or Hoopla, which can let users download e-books if they have a library card. The user might not know about these options. Also, Project Gutenberg and similar sites might have his works translated into other languages, but that's a stretch if they're modern works.
Are there any Serbian digital libraries or academic resources? The National Library of Serbia might have digitized some books. Additionally, sites like Internet Archive sometimes preserve books, but I need to verify if they have legal access.