The PDF is optimal for a complete novice in a metric country during the first 40 hours of learning. After that, it becomes a crutch.
The "2021" edition is time-sensitive. Autodesk’s 2022, 2023, and 2024 releases changed the MEP interface (e.g., the Properties palette, load calculation dialogs). A user with Revit 2024 following a 2021 PDF will encounter missing buttons, renamed tabs, and broken workflows. revit mep step by step 2021 metric edition pdf