For the file: nothing.
The file will be treated in exactly the same way.
If you try to open the file with a program then there can be a difference depending on the program.
E.g. if I use
somepictureViewer picture then there are three things which can happen:
- The program will look inside the file to determine it type. This is why many files start with something called MagicNumbers. (e.g. a JPEG file will usually start with JFIF in the first bytes. A .gif file with
GIF89. A PDF with
PDF13, etc etc. This is the clean, neat way.
- The program will try to open the file and assume it is the default format. This might leads to some messed up contents if it guesses wrong.
- The program will look at its extension and assume that a specific extension belongs to a specific file format. This can work out great and this can produce horrible results.
The most obvious example in this is with windows, where I can open a file called
demo.xls and the default settings make the assumption that a file ending in .xls is an excel file. If it is, then things work great. If it happens to be a misnamed picture (and yes, I have seen this in the wild with clueless users trying to get a picture inside an excell sheet) then things will simply go wrong.
But for the file itself: Nothing changes.