Uh... that's strange.
I did this in a quick test installation:
Page.php
static $has_one = array(
'PDF' => 'File'
);
function getCMSFields() {
$fields = parent::getCMSFields();
$fields->addFieldToTab("Root.Content.Files", new FileIFrameField('PDF'));
return $fields;
}
Template:
<div id="PcFile">
<a href="$PDF.Link">$PDF.Title</a>
</div>
Everything worked as expected, i was able to upload a .pdf and there was the correct download link showing up on the frontpage (with neat little pdf icon)
So, i am a little bit lost with your problem, sorry.
Maybe some .htaccess issues?
Cheers,
Christian