This isn't a SQLDeveloper question. You will get better answers in the Database - General forum.
Oracle dump files produced by the exp or expdp utilities are inproprietary formats which can only be read by the imp or impdp utilities respectively.
The best way to get data out of a dump file is to import it into a database and then extract it to plain text files using SQL.
Alternatively, leave it in the database and your application can access it there.
The exp dump file is mostly plain text, but the format is not published so you could waste a lot of time figuring it out.