IFilters

iFilters, or IFilters, are a family of software components that enable full-text indexing of non-text file formats by search engines and content indexing services. They extract readable text and metadata from files such as PDFs, Office documents, and other containers so their contents can be searched.

They implement the IFilter interface used by Windows Content Indexing Service and other indexers. For each registered file type, the corresponding iFilter is invoked to supply chunks of text and property values; the indexer calls methods such as Init, GetChunk, GetText, and GetValue to retrieve content and metadata.

Distribution and scope: iFilters are provided by software vendors or packaged with operating systems. Common examples include the Adobe PDF iFilter and the Microsoft Office iFilter. The available set of iFilters determines which file formats can be indexed by a given search deployment, such as Windows Search or SharePoint search.

Impact and applications: They are critical for enterprise search, enabling users to locate information inside documents rather than just file names. Without the appropriate iFilters, content inside proprietary formats remains inaccessible to the indexer and may not appear in search results.

Considerations: Administrators should ensure 32-bit versus 64-bit compatibility, keep filters up to date to support newer file formats, and manage licensing and performance trade-offs. A mismatch or outdated filters can degrade indexing effectiveness or prevent documents from being indexed properly.