I could only get that type of link to work from a web server environment e.g.
[link to page 2](http://africau.edu/images/default/sample.pdf#page=2)
I guess you could run your own web server locally and use http://localhost or similar instead of file:// ?
I know that’s a bit of a workaround, and you would have to get your local webserver to serve up the files in your vault somehow (or wherever you were storing the PDF), but I couldn’t get a file:// link to work with a tag, nor could I get it to open my web browser.
(for info, I am running Linux with Nemo as the file manager)