Are the column names exactly the same in all of the files?
Is there exactly the same number of columns in all of the files?
Are the columns in exactly the same order in all of the files?
If the answer to any of the above is no, you will probably have to rethink your approach.
If you haven't even tried to resolve your issue, please don't expect the hard-working volunteers here to waste their time providing links to answers which you could easily have found yourself.