Linking in PDFs is simpler than you might think! There are two types of links:
External Links
These of course link to external webpages. They work exactly as in HTML:
<a href="https://docraptor.com/">DocRaptor!</a>
Internal Links
This is how you link to other parts of your document. It's as simple as reference the ID of the element you'd like to link to in the URL hash, just as in HTML:
<a href="#section1">Section 1: Getting Started</a>
<div id="section1">First Section</div>