I referred to this posting and this posting, still clueless as to how to get a link to a Google Doc.
According to the offical document, webViewLink is "A link for opening the file in a relevant Google editor or viewer in a browser". However, it doesn't return anything but null, while other properties, such as id or mimeType, return expected values. (webContentLink returns null too.)
I could simply use this URL, https://drive.google.com/open?FILE_ID_HERE, but I'm not sure this works in other people's browser.
I'd appreciate any advice!