SharePoint 2010 Search Filters
There are different versions of search products that work with SharePoint 2010. The Foundation built-in search provides entry level capability and can be improved by downloading the free Search Server 2010 Express. For the SharePoint server versions, you may use the built-in Search Server 2010 (standard or enterprise) or the most advanced product – FAST search.
However, not all content formats can be crawled or indexed using out of the box functionality (meta data is no problem, but inside content is). The good news is that SharePoint search uses content filters (iFilters) which are utilities that read one or more file types. A number of filters are included with SharePoint server (see the File Types and iFilters reference from TechNet). These include office documents, text-based documents and even zip files. The MS filters are also packaged for separate download as MS Office 2010 Filter Packs (they are included in SP 2010). Some file types are not included in search by default and the previous link lists these as well. To add any additional file type (provided it has an iFilter), go to Central Admin, and Manage File Types under the relevant Search Service application.
One typical file type that has no filter is PDF. Adobe provides a 64 bit iFilter for PDF files and you can refer to a MS support article on how to download and install it (SharePoint server only, requires your farm admin intervention).
Other major vendors may have free filters for their own file types. There are also commercial providers of various iFilters like the iFilterShop.