Had a go at running this yesterday... looks good, if basic.
Looking at pdf.js website they have a demo (https://mozilla.github.io/pdf.js/web/viewer.html) which shows off a number of other features of the pdf.js plugin.
Perhaps it would be good to have a full-screen mode (a bit like the summernote editor?) which could act as an overlay.... perhaps activated by simply clicking on the pdf image, or perhaps a "preview" button?
If we went that way, then perhaps the next/previous buttons wouldn't be needed?