The microsoft-windows-netfx3-ondemand-package.cab is an original Microsoft component. Downloading it from a trusted source is not piracy; it is simply redistributing a system feature that Microsoft makes available to Windows license holders.

The .NET Framework 3.0 On Demand Package (cab) is used to:

If you have internet access and just need .NET 3.5, you can download the standard installers directly from the :

However, downloading core Windows system files from third-party sites carries security risks. It is recommended to use the following official methods to obtain the file or install .NET Framework 3.5: Official Installation Methods