Kentico can also search content of files that are in the database
https://docs.kentico.com/display/K9/Configuring+SQL+search+for+attachment+files
This would require that you create some procedure (either override the Loader Module for the media file insert, or a scheduled task) to convert your Media Files into attachments or Files in the system.
This way you don't have to 'worry' about coding the logic to 'read' the pdf and other content, leaving that to kentico, and you just worry about getting it from a File in the media library to a CMS.File object on the tree.