You need an embedded viewer, it’s not that common, most people are content with the Adobe Reader browser plugin.
I have not ever embedded a PDF viewer, you might try https://github.com/mozilla/pdf.js. This viewer is a pure HTML5/javascript implementation. At it’s most basic, your page only need provide a blank HTML canvas element, javascript handles everything else. You could create a simple page template for this, or create a custom post type. You’ll need to store the actual PDF URL somewhere associated with the page or CPT you add, a custom field would work.
You will need to add code, either as a plugin or on a child theme functions.php to enqueue the required javascript files for any pages using this template. Your enqueue script needs some way to know when to enqueue script and when not to. It could either check the post type or page template, depending on which approach you use.
You also need to pass the stored PDF URL to javascript so it knows which document to load. This can be done with wp_localize_script().