On modern systems, you don't even need a separate download. You can enable them via the Windows Features menu by checking the box for ".NET Framework 3.5 (includes .NET 2.0 and 3.0)". Historical Significance: What Changed?
This is the standard way to enable the feature without downloading files from the internet. Spiceworks Community Mount your Windows Installation Media (ISO or USB drive). Note its drive letter (e.g., Command Prompt as an Administrator. Run the following command, replacing with your actual drive letter: