When performing any search, images are returned in the search results, which is not intended. Images are attachments in WordPress, and so are PDFs. We only want PDFs in the search results, but it's including all attachments.

The fix is the apply an OR filter on all results: 
either a result is not of type `attachment`
or the result is of type `attachment` and has mime type `application/pdf`.

Tasks:

• Remove existing filters in multiple places, one of which was not working.
• Add above single filter for all results.