The Hypothes.is WordPress plugin will only work on self-hosted (.org not .com) WP sites.
You can find the Hypothes.is plugin by searching under “Plugins” in the WP admin Dashboard menu or by following this link.
Click through to install and activate it.
The Hypothes.is app will appear on any pages you want it to, including PDFs hosted at the site.
You can configure the Hypothes.is sidebar to be open or collapsed by default. And you can configure highlights to be visible or invisible by default.
Under Content Settings, Hypothes.is can be configured to be active on all posts and/or pages in a blog or only on certain ones (identified by the ID number shown in the URL when editing the post or page).
You can also configure Hypothes.is to be active on PDFs hosted on the blog. In this case, you must either have all PDFs load with Hypothes.is or none.
PDFs will be opened using the proxy server, “via.”