Confused about dynamically calling PDF files for download

I’m using Prince XML to generate PDFs into the /pdf directory and all is well.

I’m also able to statically link to a single PDF like my theme’s documentation recommends:

class="noCrossRef btn btn-default downloadPDFButton" 
role="button"><span class="glyphicon glyphicon-download-alt" 
aria-hidden="true"></span> Download PDF</button></a>```

However, I want to display the **Download PDF** button only for guides (defined in the sidebar file) that have a PDF associated with them. Here's where I'm completely lost. Should I add a custom YAML entry with the expected PDF filename that I can call on later? Should I have some sort of condition that says, "hey, if pdf output is allowed, pull out the defined PDF filename"?

I'd appreciate if anyone could point me in the right direction.