Okay, so I actually had to work out this feature for my own site anyway, and I did some research.
Apparently, there is no guarenteed, surefire way to force the PDF to be viewed in the browser. It depends on how people have configured their browser to handle PDF documents. But worstcase scenario? They will download the PDF instead of seeing it in their browser.
The common way people seem to implement it (and what seems to work in my chrome browser) is to link the document like this:
<a href="./document.pdf" target="_blank">Click here to go to go to my PDF document</a>
Note that you can specify where you have put the document by changing the href path.
A second option is PDF.js, a "Portable Document Format (PDF) viewer that is built with HTML5."
I have not tested this, but there are instructions on how to do it. Requires knowledge of how to use git.