There are certain PDF's being indexed by Search and Promote that do not have title in PDF properties set.So by default Search and Promote takes PDF file name as PDF title.
Is there way to override PDF title with some custom metadata property in AEM and have search and promote use same or using index connector with feed having title and pdf url mapping to override search results.
One way found is to use metadata injection and update title specifically for all PDF's before crawling begins.
Perhaps I am misreading, though this appears to be more of an AEM question of how to generate that feed rather than an Adobe Target question as to how to consume that meta data. You seem to be on the right track with injections/connectors/attribute loader.