Can you please clarify a bit..that what exactly you are looking for ??
Data structure of your FILE1 and FILE2 are same ?
If yes then you can use following logic to create a program.
1) Create data definition for your FILE1 record and FILE2 record.
2) Select a key( Combination of 3-4 vars) from FILE2 and do a look up in FILE1.
3) Now if match does not occur then write the record into FILE3