I need to implement a search functionality that makes the content of a PDF file indexable and links directly to the selected content area of the search query. Is that even possible and what is the way to go here?
By default, you won't be able to search the pdf file unless you use some software or script to take the data out of the pdf and put it in some place that it can be indexed and searched (or use a tool to help you).
A potential solution would be to capture and save this information on the upload of the PDF as a meta-value or similar and allow the db to index it for searching.
I would start over with a different view on the problem and seeing here for a possible nudge in the new direction: https://stackoverflow.com/questions/1004478/read-pdf-files-with-php