Just like there is a download or purchase option for Windows from their publisher (Microsoft), I could not found any download or purchase option from the official website of android (https://www.android.com/) and their owner Google.
Though there are so many third-party websites letting free download android, I don't think they are trustworthy.
I want to just know, is it possible to download or purchase Android software from any official link of their original publishers? Or the software comes only through in-built with the devices?