If you have Microsoft Excel installed on your computer, double clicking on the file will open up Excel and show you the content of the files.
Excel automatically formats the data as it imports it, and it uses some basic rules, for example, excel will try and change anything that looks like a date to date format. Excel will format anything that is a row of numbers as a number which means it may strip the leading zero, for example on a bank sort code.
You can tell Excel not to do this by importing the file. Here is a handy article that explains how to do this:
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