Previewing documents online

I have just set this doc library up and it seems to be perfect for what I want, except that I cannot view my PDFs in a preview window. I get an error with the Box plugin (https://box-content.readme.io/docs/get-started-with-the-view-api) – if I sign up to this, will everything be fixed? Or is there something else I need to do in the back end?

https://ww.wp.xz.cn/plugins/memphis-documents-library/