OK. So you want SSIS to 'interrogate' a particular file, which has already been produced by another process, get the row count and then act according to result?
If so, your question boils down to: "How can I determine how many rows there are in a text file? Is that correct?
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.