Searching for Pages (and Files)
Fulltext search for page content (and other attributes like "Title" or "MetaTags") can be easily added to SilverStripe. See Tutorial: Site Search for details.
Searching for DataObjects
The SearchContext class provides a good base implementation that you can hook into your own controllers.
A working implementation of searchable DataObjects can be seen in the
Fulltext search on DataObjects
The MySQLDatabase class now defaults to creating tables using the InnoDB storage engine. As Fulltext search in MySQL requires the MyISAM storage engine, any DataObject you wish to use with Fulltext search must be changed to use MyISAM storage engine.
You can do so by adding this static variable to your class definition:
static $create_table_options = array( 'MySQLDatabase' => 'ENGINE=MyISAM' );
Searching for Documents
SilverStripe does not have a built-in method to search through file content (e.g. in PDF or DOC format). You can either extract any textual file content into the File->Content` property, or use a dedicated search service like the sphinx module.