It depends what is that "Excel program" (what is that supposed to mean, anyway). If this is the program using Office interop, it assumes the relevant version of the Office or its part (Excel) is installed and functional. However, it could be a program not using the interop, working just based on the file format. That would not require the Office installation. To understand this approach, please see:
http://en.wikipedia.org/wiki/Microsoft_Office_XML_formats[
^],
http://en.wikipedia.org/wiki/Office_Open_XML[
^].
There are third-party libraries to work with those formats. I never used any, but you can find them if you use some search engine.
—SA
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