I'm receiving files output as .xls from I'm told Oracle. When I go to load them in Excel it warns me that they are possibly corrupt but will open them. The open file has formatted colours and once open has 1,048,576 rows. Someone else approached our inhouse Oracle admin and they were unable to help. There potentially are 100s of these to work with and consolidate so is there any way of telling what the file format genuinely is despite what the extension says?