diff --git a/source/java/org/alfresco/repo/content/transform/AbstractContentTransformer.java b/source/java/org/alfresco/repo/content/transform/AbstractContentTransformer.java
index e355888e5c..c7e8a6b106 100644
--- a/source/java/org/alfresco/repo/content/transform/AbstractContentTransformer.java
+++ b/source/java/org/alfresco/repo/content/transform/AbstractContentTransformer.java
@@ -16,6 +16,7 @@
  */
 package org.alfresco.repo.content.transform;
 
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -54,6 +55,7 @@ public abstract class AbstractContentTransformer implements ContentTransformer
     protected AbstractContentTransformer()
     {
         averageTime = 0.0;
+        explicitTransformations = new ArrayList<ContentTransformerRegistry.TransformationKey>(0);
     }
 
     /**
@@ -84,6 +86,14 @@ public abstract class AbstractContentTransformer implements ContentTransformer
         return mimetypeService;
     }
 
+    /**
+     * @return Returns the explicit transformations that were enabled for this transformer
+     */
+    protected List<ContentTransformerRegistry.TransformationKey> getExplicitTransformations()
+    {
+        return explicitTransformations;
+    }
+
     /**
      * Set the transformations that this transformer can do regardless of what it returns
      * via the {@link ContentTransformer#getReliability(String, String) reliability check}.
@@ -162,7 +172,8 @@ public abstract class AbstractContentTransformer implements ContentTransformer
     {
         String sourceMimetype = getMimetype(reader);
         String targetMimetype = getMimetype(writer);
-        if (getReliability(sourceMimetype, targetMimetype) <= 0.0)
+        double reliability = getReliability(sourceMimetype, targetMimetype);
+        if (reliability <= 0.0)
         {
             throw new AlfrescoRuntimeException("Zero scoring transformation attempted: \n" +
                     "   reader: " + reader + "\n" +
diff --git a/source/java/org/alfresco/repo/content/transform/PoiHssfContentTransformer.java b/source/java/org/alfresco/repo/content/transform/PoiHssfContentTransformer.java
index 09ff06dc76..52a6e5a8c3 100644
--- a/source/java/org/alfresco/repo/content/transform/PoiHssfContentTransformer.java
+++ b/source/java/org/alfresco/repo/content/transform/PoiHssfContentTransformer.java
@@ -16,6 +16,7 @@
  */
 package org.alfresco.repo.content.transform;
 
+import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.Map;
 
@@ -51,8 +52,6 @@ public class PoiHssfContentTransformer extends AbstractContentTransformer
      */
     private static final String LINE_BREAK = "\r\n";
     
-    private static final Log logger = LogFactory.getLog(PoiHssfContentTransformer.class);
-    
     /**
      * Currently the only transformation performed is that of text extraction from XLS documents.
      */
@@ -73,12 +72,13 @@ public class PoiHssfContentTransformer extends AbstractContentTransformer
     public void transformInternal(ContentReader reader, ContentWriter writer,  Map<String, Object> options)
             throws Exception
     {
+        InputStream is = reader.getContentInputStream();
         OutputStream os = writer.getContentOutputStream();
         String encoding = writer.getEncoding();
         try
         {
             // open the workbook
-            HSSFWorkbook workbook = new HSSFWorkbook(reader.getContentInputStream());
+            HSSFWorkbook workbook = new HSSFWorkbook(is);
             // how many sheets are there?
             int sheetCount = workbook.getNumberOfSheets();
             // transform each sheet
@@ -96,6 +96,10 @@ public class PoiHssfContentTransformer extends AbstractContentTransformer
         }
         finally
         {
+            if (is != null)
+            {
+                try { is.close(); } catch (Throwable e) {}
+            }
             if (os != null)
             {
                 try { os.close(); } catch (Throwable e) {}
diff --git a/source/java/org/alfresco/repo/content/transform/RuntimeExecutableContentTransformer.java b/source/java/org/alfresco/repo/content/transform/RuntimeExecutableContentTransformer.java
index 653b871c96..115120946b 100644
--- a/source/java/org/alfresco/repo/content/transform/RuntimeExecutableContentTransformer.java
+++ b/source/java/org/alfresco/repo/content/transform/RuntimeExecutableContentTransformer.java
@@ -18,9 +18,11 @@ package org.alfresco.repo.content.transform;
 
 import java.io.File;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import org.alfresco.error.AlfrescoRuntimeException;
+import org.alfresco.repo.content.transform.ContentTransformerRegistry.TransformationKey;
 import org.alfresco.service.cmr.repository.ContentIOException;
 import org.alfresco.service.cmr.repository.ContentReader;
 import org.alfresco.service.cmr.repository.ContentWriter;
@@ -48,6 +50,9 @@ import org.apache.commons.logging.LogFactory;
  * no effect, but may ultimately lead to the transformation failing.  This is
  * because the files provided are both temporary files that reside in a location
  * outside the system's content store.
+ * <p>
+ * This transformer <b>requires</b> the setting of the <b>explicitTransformations</b>
+ * property.
  * 
  * @see org.alfresco.util.exec.RuntimeExec
  * 
@@ -69,6 +74,16 @@ public class RuntimeExecutableContentTransformer extends AbstractContentTransfor
     {
     }
     
+    @Override
+    public String toString()
+    {
+        StringBuilder sb = new StringBuilder();
+        sb.append(this.getClass().getSimpleName())
+          .append("[ transform=").append(transformCommand).append("\n")
+          .append("]");
+        return sb.toString();
+    }
+    
     /**
      * Set the runtime executer that will be called as part of the initialisation
      * to determine if the transformer is able to function.  This is optional, but allows
@@ -134,10 +149,12 @@ public class RuntimeExecutableContentTransformer extends AbstractContentTransfor
     }
 
     /**
-     * Unless otherwise configured, this component supports all mimetypes.
      * If the {@link #init() initialization} failed, then it returns 0.0.
+     * Otherwise the explicit transformations are checked for the reliability.
      * 
      * @return Returns 1.0 if initialization succeeded, otherwise 0.0.
+     * 
+     * @see AbstractContentTransformer#setExplicitTransformations(List)
      */
     public double getReliability(String sourceMimetype, String targetMimetype)
     {
@@ -145,10 +162,23 @@ public class RuntimeExecutableContentTransformer extends AbstractContentTransfor
         {
             return 0.0;
         }
-        else
+        // check whether the transformation was one of the explicit transformations
+        TransformationKey transformationKey = new TransformationKey(sourceMimetype, targetMimetype);
+        List<TransformationKey> explicitTransformations = getExplicitTransformations();
+        if (explicitTransformations.size() == 0)
+        {
+            logger.warn(
+                    "Property 'explicitTransformations' should be set to enable this transformer: \n" +
+                    "   transformer: " + this);
+        }
+        if (explicitTransformations.contains(transformationKey))
         {
             return 1.0;
         }
+        else
+        {
+            return 0.0;
+        }
     }
     
     /**
@@ -178,13 +208,6 @@ public class RuntimeExecutableContentTransformer extends AbstractContentTransfor
                     "   target extension: " + targetExtension);
         }
         
-        // if the source mimetype is the same as the target's then just stream it
-        if (sourceMimetype.equals(targetMimetype))
-        {
-            writer.putContent(reader.getContentInputStream());
-            return;
-        }
-        
         // create required temp files
         File sourceFile = TempFileProvider.createTempFile(
                 getClass().getSimpleName() + "_source_",