gistfile1.txt

/**
 * Replace the link text with a PDF image.
 *
 * Only for an anchor link to a PDF file in field output.
 *
 * Place this code (after <?php) at the bottom of your theme's functions.php file to enable it.
 * 
 * @param string $html Existing HTML output
 * @param array $args Arguments passed to the function
 */
function modify_gravityview_field_output( $html, $args ) {

	$return = $html;
	
	// Bail if not an anchor with a PDF.
	preg_match( '/<a(.+?)>.+?(pdf)<\/a>/i', $return, $matches );
	if ( empty( $matches ) )
		return $return;
	
	// How to replace the link text with an image:
	// First, upload an image to your Media Library if necessary.
	
	// Option 1.
	// Edit the image and find the 'attachment_id' number in the Permalink.
	// Enter that number in the parentheses here:
	$image_url = '<img src="' . wp_get_attachment_url( 7 ) . '" />';
	
	// Option 2.
	// Use the name of file if you know its location in your uploads directory:
	// $image_url = '<img src="' . content_url( 'uploads/pdficon_large.png' ) . '" />';

	// Note: Linking to an external image is not recommended.
	// Official Adobe stuff: http://www.adobe.com/legal/permissions/icons-web-logos.html#weblogos
	
	// Replace the link text with the image URL.
	$return = preg_replace( '/<a(.+?)>.+?<\/a>/i', "<a$1>" . $image_url . "</a>", $return );
	
	return $return;
}
add_filter( 'gravityview_field_output', 'modify_gravityview_field_output', 10, 2 );