Storage format
The Elements Spreadsheet app stores created documents as attachments of the edited Confluence page.
Spreadsheet files saved as attachments
These attachements use the .ssc extension and the content is :
XML on Confluence Server and Data Center
JSON on Confluence Cloud
The content structure is specified to store Elements Spreadsheet documents. Consequently, a .ssc file cannot be opened with others applications like Microsoft Excel or LibreOffice Calc. We recommend you to not manually edit the content of these files, and use instead the Elements Spreadsheet editor.
If the Elements Spreadsheet app is uninstalled, or doesn't use a valid licence, the .ssc attachment files are not removed.