The method presented creates multiple Solr documents from a single content element (aka node in Drupal lingo), only applied to files. Apache Solr module provides an API to allow just that. That is what actually happens with the Apache Solr Attachments module for managed files. If a Drupal node has three attached files parsable by Tika, total of 4 Solr documents would be indexed; one node plus three files. Solr documents derived from files will show up as a search result as if they are an independent entity.