Allow link rel to be customized. Defaults to 'noreferrer'

src/display/annotation_layer.js

@@ -311,6 +311,11 @@ var AnnotationLayer = (function AnnotationLayerClosure() {
       link.target = LinkTargetStringMap[PDFJS.externalLinkTarget];
     }
 
+    // Strip referrer
+    if (item.url) {
+      link.rel = PDFJS.externalLinkRel;
+    }
+
     if (!item.url) {
       if (item.action) {
         bindNamedAction(link, item.action);

src/display/api.js

@@ -230,6 +230,14 @@ PDFJS.openExternalLinksInNewWindow = (
 PDFJS.externalLinkTarget = (PDFJS.externalLinkTarget === undefined ?
                             PDFJS.LinkTarget.NONE : PDFJS.externalLinkTarget);
 
+/**
+ * Specifies the |rel| attribute for external links. Defaults to stripping
+ * the referrer.
+ * @var {string}
+ */
+PDFJS.externalLinkRel = (PDFJS.externalLinkRel === undefined ?
+                         'noreferrer' : PDFJS.externalLinkRel);
+
 /**
   * Determines if we can eval strings as JS. Primarily used to improve
   * performance for font rendering.