The 10-K is the single most important document any public company will ever publish about itself. It is the comprehensive annual report filed with the SEC, due 60-75 days after fiscal year-end depending on company size. Unlike the glossy annual report mailed to shareholders (which is marketing), the 10-K is a legal document.

Companies can be — and are — sued for misstatements in their 10-K. SEC staff review them. Auditors sign the financial statements with their professional liability on the line.

Reading the 10-K, before any analyst report or earnings call transcript, is the foundational discipline of fundamental investing. Most retail investors never open one. The cost of that habit is the gap between professionals and amateurs.

A 10-K runs 100-300+ pages, organized into four parts. Part I starts with Item 1 (Business — what the company does, its segments, its customers, its competition) and Item 1A (Risk Factors — everything management is legally required to disclose could go wrong).