open pdf in main container

I had a static site that allowed a left column with links to newsletters.
When I clicked those links pdf.js would open in another div beside the left column (main container) I cannot recreate that experience in WordPress. Has anyone figured this out?
Example of what I had:

<div class="nb-left_column">
<a class="gnb-link" href="001Newsletter.pdf">Dec Newsletter</a></br>
<a class="gnb-link" href="002Newsletter.pdf">Nov Newsletter</a></br>
<a class="gnb-link" href="003Newsletter.pdf">Oct Newsletter</a></br>
</div>
<div class="nb-viewing_container" id="pdf-container">
<h3>News Bulletin</h3>
<p>Click link on the left to open new bulletin. </p>
</div>