scroll up and down in Preview using J and K

private.xml

<?xml version="1.0"?>
<root>
  <item>
    <name>Enable at only Preview</name>
    <item>
      <name>Change J to Down</name>
      <identifier>remap.app_preview_j2Down</identifier>
      <only>PREVIEW</only>
      <autogen>--KeyToKey-- KeyCode::J, KeyCode::CURSOR_DOWN</autogen>
    </item>
    <item>
      <name>Change K to Up</name>
      <identifier>remap.app_preview_k2Up</identifier>
      <only>PREVIEW</only>
      <autogen>--KeyToKey-- KeyCode::K, KeyCode::CURSOR_UP</autogen>
    </item>
    <item>
      <name>Change G to Home</name>
      <identifier>remap.app_preview_g2Home</identifier>
      <only>PREVIEW</only>
      <autogen>--KeyToKey-- KeyCode::G, KeyCode::HOME</autogen>
    </item>
    <item>
      <name>Change Shitf+G to End</name>
      <identifier>remap.app_preview_shift_g_2End</identifier>
      <only>PREVIEW</only>
      <autogen>--KeyToKey-- KeyCode::G, VK_SHIFT, KeyCode::END</autogen>
    </item>
  </item>
</root>