Empty Iframe when using shortcode

I’m unsure as to why, as I’ve searched through all of the documentation.

When displaying the shortcode, I simply get a blank PDF doc. I’ve triple checked my paths, have disabled all plugins, changed themes, etc., and the result is still the same.

Note: My site is SSL’d, so I’ve tried 3 different versions of the plugin’s shortcode:
[pdfjs-viewer url=https://https://www.website.com/test.pdf viewer_width=600px viewer_height=700px fullscreen=true download=true print=true openfile=false]
[pdfjs-viewer url=https://https://www.website.com/test.pdf viewer_width=600px viewer_height=700px fullscreen=true download=true print=true openfile=false]
[pdfjs-viewer url=//https://www.website.com/test.pdf viewer_width=600px viewer_height=700px fullscreen=true download=true print=true openfile=false]

Perhaps the only thing that’s different is I don’t upload my documents to the WordPress media library; I keep them in various folders (e.g., root/sealed-files/ or root/docs/, etc.).

Here’s a screen capture on what I’m seeing.

I’d really like to get this working, as it’s compatible with a lightbox plugin I’m using, so any guidance in helping me with this issue would be greatly appreciated!

https://www.ads-software.com/plugins/pdfjs-viewer-shortcode/