Double-entry: Every transaction affects at least two accounts; debits = credits.
When downloading PDFs from third-party sites, be cautious and aware of potential malware risks.
Consider the legality and ethics of accessing copyrighted materials. Many authors and publishers rely on book sales to support their work.
Google Books: Offers previews of books. You might find a digital version but might not be able to access the full content for free.
ResearchGate or Academia.edu: Scholars sometimes upload their personal copies or references to their work here. You might find a PDF if someone has shared it.
Income Statement: Revenues − Expenses = Net Income.