Web Share API - Share files from server

I want to create a website to share files to a WhatsApp chat. This should be possible in chrome by using the Web Share API https://developers.google.com/web/updates/2019/05/web-share-files The demo in the description works but only with files uploaded with the form. In my case, the files are already on the server. Has anyone done this before and can help me with the code? Thanks! Daniel