Duplicate data in a table given table name

For a performance testing application we need to have lot more data in our tables than what we have now. How do I duplicate the data in a table.

In the process of duplicating I also need to set new values for primary key column. I'm thinking getting the max value of primary key column and adding a incrementing number to it will solve the primary key issue.

Is it possible to do this in PL/SQL.