Hi Rohit,
What u have to do is;
1) first you save the internal patterns in .wgl format (I think u r looking for this format). This you
have to do during the pattern generation time.
Command: cmd1) set patterns internal
cmd2) run atpg
cmd3) write patterns pattern_file.pat -internal -format wgl
2) Then modify the existing patterns with the external pattern
of your interest and then simulate.
Few Definition: External patterns are those patterns which are generated by user. They can be applied to Tmax latter for simulation purpose. Internal patterns are those which Tmax can genrate for user.