diff --git a/CMakeLists.txt b/CMakeLists.txt
index dc9a9540b..e9dc22275 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -36,6 +36,7 @@ set(okularcore_SRCS
    core/document.cpp
    core/generator.cpp
    core/link.cpp
+   core/observer.cpp
    core/page.cpp
    core/pagetransition.cpp
    core/rotationjob.cpp
diff --git a/core/observer.cpp b/core/observer.cpp
new file mode 100644
index 000000000..6a4a95e53
--- /dev/null
+++ b/core/observer.cpp
@@ -0,0 +1,42 @@
+/***************************************************************************
+ *   Copyright (C) 2005 by Enrico Ros <eros.kde@email.it>                  *
+ *   Copyright (C) 2005 by Albert Astals Cid <tsdgeos@terra.es>            *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ ***************************************************************************/
+
+#include "observer.h"
+
+using namespace Okular;
+
+DocumentObserver::~DocumentObserver()
+{
+}
+
+void DocumentObserver::notifySetup( const QVector< Okular::Page * >&, bool )
+{
+}
+
+void DocumentObserver::notifyViewportChanged( bool )
+{
+}
+
+void DocumentObserver::notifyPageChanged( int, int )
+{
+}
+
+void DocumentObserver::notifyContentsCleared( int )
+{
+}
+
+void DocumentObserver::notifyVisibleRectsChanged()
+{
+}
+
+bool DocumentObserver::canUnloadPixmap( int ) const
+{
+    return true;
+}
diff --git a/core/observer.h b/core/observer.h
index 857c92722..db0faa0de 100644
--- a/core/observer.h
+++ b/core/observer.h
@@ -52,7 +52,7 @@ class DocumentObserver
         /**
          * Destroys the document observer.
          */
-        virtual ~DocumentObserver() {};
+        virtual ~DocumentObserver();
 
         /**
          * Must return an unique ID for each observer (used for notifications).
@@ -83,14 +83,49 @@ class DocumentObserver
             VisibleAreas = 16     ///< The visible are changed
         };
 
-        virtual void notifySetup( const QVector< Okular::Page * > &/*pages*/, bool /*documentChanged*/ ) {};
-        virtual void notifyViewportChanged( bool /*smoothMove*/ ) {};
-        virtual void notifyPageChanged( int /*pageNumber*/, int /*changedFlags*/ ) {};
-        virtual void notifyContentsCleared( int /*changedFlags*/ ) {};
-        virtual void notifyVisibleRectsChanged() {};
+        /**
+         * This method is called whenever the document is initialized or reconstructed.
+         *
+         * @param pages The vector of pages of the document.
+         * @param documentChanged If true, the document is reconstructed.
+         */
+        virtual void notifySetup( const QVector< Okular::Page * > &pages, bool documentChanged );
+
+        /**
+         * This method is called whenever the viewport has been changed.
+         *
+         * @param smoothMove If true, the move shall be animated.
+         */
+        virtual void notifyViewportChanged( bool smoothMove );
+
+        /**
+         * This method is called whenever the content on @p page described by the
+         * passed @p flags has been changed.
+         */
+        virtual void notifyPageChanged( int page, int flags );
+
+        /**
+         * This method is called whenever the content described by the passed @p flags
+         * has been cleared.
+         */
+        virtual void notifyContentsCleared( int flags );
+
+        /**
+         * This method is called whenever the visible rects have been changed.
+         */
+        virtual void notifyVisibleRectsChanged();
+
+        /**
+         * Returns whether the observer agrees that all pixmaps for the given
+         * @p page can be unloaded to improve memory usage.
+         *
+         * Returns true per default.
+         */
+        virtual bool canUnloadPixmap( int page ) const;
 
-        // queries to observers
-        virtual bool canUnloadPixmap( int /*pageNum*/ ) const { return true; }
+    private:
+        class Private;
+        Private* d;
 };
 
 }