Index: src/wp-admin/css/media.css
===================================================================
--- src/wp-admin/css/media.css	(revision 39184)
+++ src/wp-admin/css/media.css	(working copy)
@@ -769,7 +769,7 @@
 
 .edit-attachment-frame .attachment-media-view .details-image {
 	display: block;
-	margin-bottom: 16px;
+	margin: 0 auto 16px;
 	max-width: 100%;
 	max-height: 90%;
 	max-height: -webkit-calc( 100% - 42px );
@@ -776,6 +776,10 @@
 	max-height: calc( 100% - 42px ); /* leave space for actions underneath */
 }
 
+.edit-attachment-frame .attachment-media-view .attachment-actions {
+	text-align: center;
+}
+
 .edit-attachment-frame .wp-media-wrapper {
 	margin-bottom: 12px;
 }
Index: src/wp-includes/media-template.php
===================================================================
--- src/wp-includes/media-template.php	(revision 39184)
+++ src/wp-includes/media-template.php	(working copy)
@@ -325,6 +325,8 @@
 				<div class="attachment-actions">
 					<# if ( 'image' === data.type && ! data.uploading && data.sizes && data.can.save ) { #>
 					<button type="button" class="button edit-attachment"><?php _e( 'Edit Image' ); ?></button>
+					<# } else if ( 'pdf' === data.subtype && data.sizes ) { #>
+					<?php _e( 'Thumbnail Preview' ); ?>
 					<# } #>
 				</div>
 			</div>