diff --git a/canvasblocker.xpi b/canvasblocker.xpi
index 37d4286..c0a4034 100644
Binary files a/canvasblocker.xpi and b/canvasblocker.xpi differ
diff --git a/data/inject.js b/data/inject.js
index d934baf..02ba040 100644
--- a/data/inject.js
+++ b/data/inject.js
@@ -1,38 +1,51 @@
 var getContext = unsafeWindow.HTMLCanvasElement.prototype.getContext;
 var askFunctionName = Math.random().toString(16);
 
-function block(){
-	// consoe.log("block");
-	delete unsafeWindow.HTMLCanvasElement.prototype[askFunctionName];
-	unsafeWindow.HTMLCanvasElement.prototype.getContext = null;
+function checkPDF(blocking){
+	if (unsafeWindow.document.contentType.match(/\/pdf$/i)){
+		self.port.emit("isPDF", blocking);
+		return false;
+	}
+	return true;
 }
-function ask(){
-	// console.log("ask");
-	
-	Object.defineProperty(
-		unsafeWindow.HTMLCanvasElement.prototype,
-		askFunctionName,
-		{
-			value: getContext,
-			enumerabe: false
-		}
-	);
-	unsafeWindow.HTMLCanvasElement.prototype.getContext = new unsafeWindow.Function(function(){
-		var oldBorder = this.style.border;
-		this.style.border = "2px dashed red";
-		var confirmText =
-			this.parentNode?
-			"Do you want to allow the red bordered <canvas>?":
-			"Do you want to allow an invisibe <canvas>?";
-		var allow = confirm(confirmText);
-		this.style.border = oldBorder;
-		if (allow){
-			return this["askFunctionName"].apply(this, arguments);
-		}
-		else {
-			return null;
-		}
-	}.toString().replace(/^function\s*\(\)\s*\{|\}\s*$/g, "").replace("askFunctionName", askFunctionName));
+
+function block(force){
+	if (force || !checkPDF("block")){
+		// consoe.log("block");
+		delete unsafeWindow.HTMLCanvasElement.prototype[askFunctionName];
+		unsafeWindow.HTMLCanvasElement.prototype.getContext = null;
+	}
+}
+function ask(force){
+	if (force || !checkPDF("ask")){
+		// console.log("ask");
+		
+		Object.defineProperty(
+			unsafeWindow.HTMLCanvasElement.prototype,
+			askFunctionName,
+			{
+				value: getContext,
+				enumerabe: false
+			}
+		);
+		unsafeWindow.HTMLCanvasElement.prototype.getContext = new unsafeWindow.Function(function(){
+			var oldBorder = this.style.border;
+			this.style.border = "2px dashed red";
+			var confirmText =
+				this.parentNode?
+				"Do you want to allow the red bordered <canvas>?":
+				"Do you want to allow an invisibe <canvas>?";
+			var allow = confirm(confirmText);
+			this.style.border = oldBorder;
+			if (allow){
+				this.getContext = this["askFunctionName"];
+				return this["askFunctionName"].apply(this, arguments);
+			}
+			else {
+				return null;
+			}
+		}.toString().replace(/^function\s*\(\)\s*\{|\}\s*$/g, "").replace(/askFunctionName/g, askFunctionName));
+	}
 }
 function unblock(){
 	// console.log("unblock");
diff --git a/lib/main.js b/lib/main.js
index 8dea053..11ead3e 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -88,6 +88,10 @@ preferences.on("askPermission", function(){
 	}
 	workers.forEach(checkWorker);
 });
+preferences.on("allowPDFCanvas", function(){
+	workers.forEach(checkWorker);
+});
+
 
 pageMod.PageMod({
 	include: "*",
@@ -100,5 +104,13 @@ pageMod.PageMod({
 		worker.on("detach", function(){
 			detachWorker(this, workers);
 		});
+		worker.port.on("isPDF", function(blocking){
+			if (prefs.allowPDFCanvas){
+				worker.port.emit("unblock");
+			}
+			else {
+				worker.port.emit(blocking, true);
+			}
+		});
 	},
 });
\ No newline at end of file
diff --git a/package.json b/package.json
index 59ebd2b..a01241f 100644
--- a/package.json
+++ b/package.json
@@ -31,6 +31,13 @@
 			"description": "If you want to be asked if you want to block a canvas element if the domain is neither in the white or black list.",
 			"type": "bool",
 			"value": true
+		},
+		{
+			"name": "allowPDFCanvas",
+			"title": "Allow canvas in PDFs.",
+			"description": "The native pdf.js uses <canvas> to display the PDF content. If this is unchecked there will lots of annoying ask dialogs.",
+			"type": "bool",
+			"value": true
 		}
 	],
 	"author": "Korbinian Kapsner",