1. copy template file /wp-content/plugins/pdf-light-viewer/templates/shortcode-pdf-light-viewer.php to your current theme folder:
2. add html somewhere inside <div class=”pdf-light-viewer js-pdf-light-viewer”> tag inside template:

<a href="#!" title="Previous" class="pdf-light-viewer-previous-page js-pdf-light-viewer-previous-page">
 <i class="icons slicon-arrow-left"></i>
</a>
<a href="#!" title="Next" class="pdf-light-viewer-next-page js-pdf-light-viewer-next-page">
 <i class="icons slicon-arrow-right"></i>
</a>

3. Add css styles:

.pdf-light-viewer-previous-page {
 position: absolute;
 left: -50px;
 top: 50%;
 font-size: 70px;
}
 
.pdf-light-viewer-next-page {
 position: absolute;
 right: -50px;
 top: 50%;
 font-size: 70px;
}

In result you should receive something similar to this

Original question: https://support.wp.teamlead.pw/q/how-to-show-nextprevious-page-arrows-at-rightleft-edges-of-book/