You just simply need to put the shortcode into your site, and it will do the job.
Upload your PDF to Media Library
Make a new post at the Lightbox PDF menu
Set the title, thumbnail, select an mp3 file and select a pdf file
Check the ID of the created PDF post
Put the shortcode wherever you need
The shortcode looks like this:
[lbpdfviewr id={ID of the LightBox PDF you want} type={button / thumbnail} audio={true / false} class=”{custom css class}”]