QnA Maker supports automatic extraction of question-and-answer pairs from structured files such as PDF, Microsoft Word, or Excel documents, as well as from public webpages. This makes PDF the correct file format for populating a knowledge base. Other options are invalid: * B. PPTX - Not supported. * C. XML - Not a recognized input for QnA Maker. * D. ZIP - Used for packaging, not Q&A content.