IFilter : Used for extracting text from files

Microsoft Search uses IFilters (aka filter) to extract text and metadata out of documents. IFilters are COM Objects that implement the IFilter interface. Example of an IFilter is an html filter. The html filter is capable of extracting the text in html documents. In addition to text, it can also emit metadata like titles and links. MSDN documents the IFilter COM interface.

For a list of IFilters develped by Independent Software Vendors, please see https://addins.msn.com/