Download the Local Help
To download the complete Inventor 2016 Help System to your computer or local network for installation, click an installer for the supported language below.
NOTE: You can specify whether to access the ONLINE help or the downloaded/LOCAL Help as your default from within Inventor. After you install the local help, you can switch between it and online Help any time. Set the Help Options in the Application Options dialog box, General tab.
For more information, please visit the Autodesk Help page here: