Once you have your SharePoint server up and running and begin to build up a corpus of content, you may find that certain documents aren’t turning up in searches. This may be due to not having the appropriate iFilters installed. From the Wikipedia entry:
IFilters are plugins that allow the Windows Indexing Service and the newer Windows Desktop Search to index different various file formats so that they become searchable. Without an appropriate IFilter, contents of a file cannot be indexed.
Here are a few important ones. If your organization uses a particular type of file frequently, make sure to look into the iFilter for it. The Wikipedia article above has links to many free and for-pay iFilters. Note that there may be different versions of iFilters for 32-bit vs. 64-bit operating systems, different file versions, etc., so be sure to get the right ones for your needs.
2007 Office System Converter: Microsoft Filter Pack – This download will install and register IFilters with the Windows Indexing Service. These IFilters are used by Microsoft Search products to index the contents of specific document formats. This Filter Pack includes IFilters for the following formats: .docx, .docm, .pptx, .pptm, .xlsx, .xlsm, .xlsb, .zip, .one, .vdx, .vsd, .vss, .vst, .vdx, .vsx, and .vtx.
Adobe PDF IFilter v6.0 or Adobe PDF iFilter 9 for 64-bit platforms – Adobe® PDF iFilter is designed for end users or administrators who wish to index Adobe PDF documents using Microsoft indexing clients. This allows the user to easily search for text within Adobe PDF documents.