The jagged arrow in the icon indicates a link to a file that’s not in the body of the database.
How did you import the files? That icon indicates use of File > Link to. If you did that, DT did not import any text within the PDF files.
If you wish to search and analyze the text of PDF documents, you should use File > Import > Files & Folders, with appropriate settings in DT or DT Pro Preferences > PDF & PS.