I have been wondered following: Excel and Word are closed source product. But still, Libreoffice can write Excel and Word documents, at least to some extent. Is it true that it is not criminal to figure out how a closed source program works and implement an open source alternative to it? Or has Microsoft opened some parts of the file formats to developers?

  • Why do you think it should be criminal to figure out how something works?
    – user253751
    Feb 18, 2020 at 15:31

1 Answer 1


Word and Excel files are stored in Open Office XML format1

As the name suggests, this is an open format - specifically, it’s a bunch of zipped XML text files. Change the extension of any office file to .xml and you can open them with any zip program.

1Since 2007.

However, that begs the question ...

Copyright law allows reverse engineering, particularly when the info contained in the file is your info as it is in any type of save file.

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