Use this skill the moment a file path appears under /mnt/user-data/uploads/, inside an uploaded_files block, inside a file_path tag, or when the user says "the file I uploaded", "the attached document", or "the file I sent". This skill is a router: it tells you WHICH tool or library to use for each file type (pdf, docx, xlsx, csv, json, images, zip, epub, pptx) so you always read content correctly. Trigger BEFORE attempting to open any uploaded file. Do NOT use this skill if the file content is already visible in a <documents> block — you already have it; skip directly to answering.