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You do not need any special software to save your document in an open format.
The software we use every day, Software such as Microsoft Office Suite, will 'automatically' save your document in a closed format like Excel Spreadsheet (.XLS).
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But you have the option to save in an open format alternative using the Save as... drop down menu.
For example, OpenDocument Spreadsheet (ODS format) can be used for spreadsheets and reports.
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