Oz Warren

At a high level, all you need to do is get the icon into the \template\images directory, and then map the extension to the icon in \template\xml\docicon.xml.  Then you reset IIS, and voilà, you have your mapping.

So, let's say you've already dropped icpdf.gif into the \template\images directory.  You would then modify docicon.xml to add the mapping that points to the icon (in bold below):

<DocIcons>
  <ByProgID>
    <Mapping Key="Excel.Sheet" Value="ichtmxls.gif"/>
    <Mapping Key="PowerPoint.Slide" Value="ichtmppt.gif"/>
    <Mapping Key="Word.Document" Value="ichtmdoc.gif"/>
  </ByProgID>
  <ByExtension>
    <Mapping Key="doc" Value="icdoc.gif"/>
    <Mapping Key="gif" Value="icgif.gif"/>
    <Mapping Key="htm" Value="ichtm.gif"/>
    <Mapping Key="html" Value="ichtm.gif"/>
    <Mapping Key="ppt" Value="icppt.gif"/>
    <Mapping Key="pdf" Value="icpdf.gif"/>
  </ByExtension>
</DocIcons>

Now, let's say you also want to add a new default icon for unknown file types, called icunk.gif. Again, you'd drop the icon in the \template\images directory, but this time you'd modify docicon.xml to add a default value that is used if a matching can't be made by ProgID or Extension (in bold below):