<ul class="itemAttachments">
  	    <?php foreach ($this->item->attachments as $attachment): ?>
  	    <li>
  		    <a title="<?php echo K2HelperUtilities::cleanHtml($attachment->titleAttribute); ?>" href="<?php echo $attachment->link; ?>">

            <?php
              $mystring = $attachment->title;
              $findme = '.pdf';
              $pos = strpos($mystring, $findme);

              // Note our use of ===. Simply == would not work as expected
              // because the position of 'a' was the 0th (first) character.
              if ($pos ===  true) {
              echo '<i class="fa fa-file-word-o" aria-hidden="true"></i>';

              } else {
              echo'<i class="fa fa-file-pdf-o" aria-hidden="true"></i>';
              }
            ?>

            <?php echo $attachment->title; ?>
          </a>
  		    <?php if($this->item->params->get('itemAttachmentsCounter')): ?>
  		    <span>(<?php echo $attachment->hits; ?> <?php echo ($attachment->hits==1) ? JText::_('K2_DOWNLOAD') : JText::_('K2_DOWNLOADS'); ?>)</span>
  		    <?php endif; ?>
  	    </li>
  	    <?php endforeach; ?>
  	  </ul>

$attitle = $attachment->title;

// Filenames
$pdf = '.pdf';
$doc = '.doc';
$xls = '.xls';
$ppt = '.pp';

// Check to see which filename is found
$foundpdf = strpos($pdf, $attitle);
$founddoc = strpos($doc, $attitle);
$foundxls = strpos($xls, $attitle);
$foundppt = strpos($ppt, $attitle);

// Note our use of ===. Simply == would not work as expected
// because the position of 'a' was the 0th (first) character.
if ($foundpdf ===  true) 
{
	echo '<i class="fa fa-file-pdf-o" aria-hidden="true"></i>';

} 
elseif ( $founddoc === true ) 
{
	echo'<i class="fa fa-file-word-o" aria-hidden="true"></i>';
} 
elseif ( $foundxls === true ) 
{
	// DO SOMETHING
}
elseif ( $foundppt === true ) 
{
	// DO SOMETHING
}
else 
{
	// DEFAULT BEHAVIOUR	
}