How would you design a web app that guides product managers through creating software requirements documents step-by-step, with validation and export features?

Build a multi-step wizard that helps product managers formulate a complete software requirements document. Each step guides the user to formulate one section: problem statement, target users, functional requirements, non-functional requirements, and acceptance criteria. Validate that each section is substantive before allowing progression to the next step. At the end, combine all sections into a downloadable Markdown file.