C# Definition:

[ComImport, Guid("89BCB740-6119-101A-BCB7-00DD010655AF")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IFilter
{
   /// <summary>
   /// The IFilter::Init method initializes a filtering session.
   /// </summary>
   [PreserveSig]
   IFilterReturnCodes Init(
     //[in] Flag settings from the IFILTER_INIT enumeration for
     // controlling text standardization, property output, embedding
     // scope, and IFilter access patterns.
     IFILTER_INIT grfFlags,

     // [in] The size of the attributes array. When nonzero, cAttributes
     //  takes
     // precedence over attributes specified in grfFlags. If no
     // attribute flags
     // are specified and cAttributes is zero, the default is given by
     // the
     // PSGUID_STORAGE storage property set, which contains the date and
     //  time
     // of the last write to the file, size, and so on; and by the
     //  PID_STG_CONTENTS
     // 'contents' property, which maps to the main contents of the
     // file.
     // For more information about properties and property sets, see
     // Property Sets.
     int cAttributes,

     //[in] Array of pointers to FULLPROPSPEC structures for the
     // requested properties.
     // When cAttributes is nonzero, only the properties in aAttributes
     // are returned.
     IntPtr aAttributes,

     // [out] Information about additional properties available to the
     //  caller; from the IFILTER_FLAGS enumeration.
     ref IFILTER_FLAGS pdwFlags);

   /// <summary>
   /// The IFilter::GetChunk method positions the filter at the beginning
   /// of the next chunk,
   /// or at the first chunk if this is the first call to the GetChunk
   /// method, and returns a description of the current chunk.
   /// </summary>
   [PreserveSig]
   IFilterReturnCodes GetChunk(ref STAT_CHUNK pStat);

   /// <summary>
   /// The IFilter::GetText method retrieves text (text-type properties)
   /// from the current chunk,
   /// which must have a CHUNKSTATE enumeration value of CHUNK_TEXT.
   /// </summary>
   [PreserveSig]
   IFilterReturnCodes GetText(
       // [in/out] On entry, the size of awcBuffer array in wide/Unicode
       // characters. On exit, the number of Unicode characters written to
       // awcBuffer.
       // Note that this value is not the number of bytes in the buffer.
       ref int pcwcBuffer,

       // Text retrieved from the current chunk. Do not terminate the
       // buffer with a character.  
       [Out(), MarshalAs(UnmanagedType.LPWStr)]
       StringBuilder awcBuffer);

   /// <summary>
   /// The IFilter::GetValue method retrieves a value (public
   /// value-type property) from a chunk,
   /// which must have a CHUNKSTATE enumeration value of CHUNK_VALUE.
   /// </summary>
   [PreserveSig]
   IFilterReturnCodes GetValue(
       // Allocate the PROPVARIANT structure with CoTaskMemAlloc. Some
       // PROPVARIANT
       // structures contain pointers, which can be freed by calling the
       // PropVariantClear function.
       // It is up to the caller of the GetValue method to call the
       //   PropVariantClear method.            
       // ref IntPtr ppPropValue
       // [MarshalAs(UnmanagedType.Struct)]
       ref IntPtr PropVal);

   /// <summary>
   /// The IFilter::BindRegion method retrieves an interface representing
   /// the specified portion of the object.
   /// Currently reserved for future use.
   /// </summary>
   [PreserveSig]
   IFilterReturnCodes BindRegion(ref FILTERREGION origPos,
     ref Guid riid, ref object ppunk);
}

VB Definition:

   TODO

User-Defined Types:

IFILTER_FLAGS, IFilterReturnCodes, STAT_CHUNK, FILTERREGION

Notes:

None.