Display value of custom field (but not in undordered list)

Yes, I know about the_meta(). In this case, I don’t want to do that. I need to dynamically insert the value of a custom field into an a href link. Something like this:

<a href="pdf/completions/<?php name_of_custom_field()?>.zip">Custom Field Link</a><br />

but I can’t figure out the proper way to do it. I’m not looking for anything elaborate. There’s only one custom field and only one value. No more. So what’s the proper PHP code to make this work?