How to sneakily download files onto end-users' computers OR record their screens without them noticing?

I am building a web application which will be a SaaS tool. There is one important thing I need to implement. As soon as the user visits my web page, and clicks the 'Start Now' button, I need to automatically download certain files on the user's computer irrespective of whether the user has enabled or disabled automatic downloads in their settings; this is a web browser based game, so the UX has to be seamless. How do I achieve this?