Make an effort to adhere the spec 7.6.3.2

src/api.js

@@ -295,7 +295,7 @@ var PDFPageProxy = (function PDFPageProxyClosure() {
           }
 
           var gfx = new CanvasGraphics(params.canvasContext, this.commonObjs,
-            this.objs, params.textLayer);
+            this.objs, !this.pageInfo.disableTextLayer && params.textLayer);
           try {
             this.display(gfx, params.viewport, complete, continueCallback);
           } catch (e) {

src/crypto.js

@@ -560,6 +560,7 @@ var CipherTransformFactory = (function CipherTransformFactoryClosure() {
     var ownerPassword = stringToBytes(dict.get('O'));
     var userPassword = stringToBytes(dict.get('U'));
     var flags = dict.get('P');
+    this.disableTextLayer = !(flags & 16);
     var revision = dict.get('R');
     var encryptMetadata = algorithm == 4 &&  // meaningful when V is 4
       dict.get('EncryptMetadata') !== false; // makes true as default value

src/worker.js

@@ -212,11 +212,13 @@ var WorkerMessageHandler = {
     handler.on('GetPageRequest', function wphSetupGetPage(data) {
       var pageNumber = data.pageIndex + 1;
       var pdfPage = pdfModel.getPage(pageNumber);
+      var encrypt = pdfModel.xref.encrypt;
       var page = {
         pageIndex: data.pageIndex,
         rotate: pdfPage.rotate,
         ref: pdfPage.ref,
-        view: pdfPage.view
+        view: pdfPage.view,
+        disableTextLayer: encrypt ? encrypt.disableTextLayer : false
       };
       handler.send('GetPage', {pageInfo: page});
     });