PHP help — Skip code if Custom Field has no value

Hello there. I’m using custom fields to display information about press clippings. I’ve got four — date, publication, PDF, and Link.

I have the template spit out a little PDF icon linking to the PDF version and the text “LINK” linking to the online version of a clipping.

This is working wonderfully, but some of my clippings do not have either a PDF version or a link, and these fields are empty. The template then generates an icon/link that links to nothing. How can I get this code to skip the custom field if it is empty?

My code:

<?php if ( in_category('3') ): ?>
<span class="caps" style="font-size: 8pt">
>>Published <?php echo get_post_meta($post->ID, 'Date', true); ?> in <?php echo get_post_meta($post->ID, 'Publication', true); ?>.
<a href="<?php echo get_post_meta($post->ID, 'PDF', true); ?>"><img src="/images/pdficon.gif" border="0"></a>
<a href="<?php echo get_post_meta($post->ID, 'Link', true); ?>">LINK</a>
<br><br>
</span>
<?php endif; ?>