Finding the Filter DLL for a File


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The following example, for HTML files, shows how to find the filter DLL for a document.

To find the filter DLL for a document:

  1. Determine the persistent handler registered for an extension. Check to see whether the extension for the type of files that the DLL filters has a persistent handler registered under the registry entry \HKEY_LOCAL_MACHINE\SOFTWARE\Classes. Let this be <Value1>.

  2. If this entry exists, skip to step 4 and use <Value1> there.

    Alternatively, determine the CLSID. If there is not a persistent handler registered for the extension, find the CLSID associated with the document type under the registry entry \HKEY_LOCAL_MACHINE\SOFTWARE\Classes. Let this be <Value2>.

            = Class for WWW HTML files
                = {25336920-03F9-11CF-8FD0-00AA00686F13}
  3. Determine the persistent handler. Using <Value2>determined in Step 2, find the PersistentHandler value for the \HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\<Value2> entry. Let this be <Value3>.

                = WWW HTML files
                    = {EEC97550-47A9-11CF-B952-00AA0051FE20}
  4. Determine the IFilter persistent handler GUID. Using <Value1> determined in Step 1 or <Value3> determined in Step 3, find the IFilter Persistent Handler GUID for the document type. The value under the registry entry

    \HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\<Value1 or 3>\PersistentAddinsRegistered\

    89BCB740-6119-101A-BCB7-00DD010655AF yields the IFilter Persistent Handler GUID for this document type. Let this be <Value4>. 89BCB740-6119-101A-BCB7-00DD010655AF is the IFilter interface GUID.

                 = REG_SZ HTML File Persistent Handler
                     = REG_SZ {E0CA5340-4534-11CF-B952-00AA0051FE20}
  5. Determine the filter DLL. Using <Value4> determined in Step 4, the filter DLL can be found under the entry


            = REG_SZ HTML Filter
                = REG_SZ nlhtml.dll

In this example, the filter DLL for HTML documents is nlhtml.dll