Web content manager allows filters on web content items only. See the article “Defining seedlist filters for WebSphere Portal and Web Content Management” (http://www-10.lotus.com/ldd/portalwiki.nsf/dx/Defining_seedlist_filters_for_WebSphere_Portal_and_Web_Content_Management). However there is no option provided to specifically select file resource elements as to whether it should be added to the search index or not.
What is documented and possible is to make use of a WCM search service property setting which is used to specify if file attachments are listed in a WCM seedlist in general or not. See chapter “Configuring Web Content Manager search options” (http://www-01.ibm.com/support/knowledgecenter/SS3JLV_8.0.0/wcm/wcm_config_search.dita) in the product's Knowledge Center:
Yet there is also the formerly undocumented option to exclude attachments based on their file extension from being included in the WCM seedlist by listing their file extensions. The property's name is:
This property can be assigned a comma delimited string of file extensions. As an example:
will exclude any file resource from being included in the Seeedlist which has one of the three above mentioned file extensions (mpeg, zip and gz).