If you don't need .dat extension why do you specify it in the first place?

>>What's wrong with the current approach? Did you examine the content of the new file? What's wrong with it?
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>The contents of the new file are OK. Whats wrong with it it that this file will be picked up by the paying agency and processed and they want is as an ordinary "file" and not a file with an extension such as .dat.
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>Thanks.