The file is found within the Windows ISO or installation media under the \sources\sxs Where to find microsoft-windows-netfx3-ondemand-package.cab
So you search for a solution, and you stumble upon a file named microsoft-windows-netfx3-ondemand-package.cab . But then you see a variation: microsoft-windows-netfx3-ondemand-package.cab -Extra . Microsoft-windows-netfx3-ondemand-package.cab -Extra
To understand the .cab file, we first need to understand how Windows architecture has changed. The file is found within the Windows ISO
PowerShell offers a more modern approach to the same task. Microsoft-windows-netfx3-ondemand-package.cab -Extra
However, your query is a bit ambiguous because of the part. This could refer to a few different things in a technical context: