It would be nice to see a second link in the help menu. But I will say, though I do like visually scanning through the manual, searching is much better using the online help docs. You can also use Google to find things.
That said, here’s a cludgy solution, and the results depend on your browser settings. And to actually do it requires some specialized knowledge. (I can’t help with that 
)
Change the contents of the file dickiedrummer mentioned.
Change the first url that appears in the file to “C:\Program Files\Steinberg\Cubase 9\Documentation\Operation_Manual.pdf”