Visibility is a property, not a privacy boundary
A hidden sheet is still part of the workbook. The default extraction includes it because supporting data may be essential, but the preview labels visible, hidden and very hidden sheets. Review those labels before sharing the converted package. Selecting only visible sheets is an explicit filtering choice, not a claim that the remaining cells contain no private information.
If you select only hidden sheets, the new workbook still needs one visible sheet to open normally. The first selected sheet is therefore made visible and that change is recorded. The original workbook and its visibility settings are never modified.
Dates need the original workbook context
Excel stores many dates as numbers interpreted through a number format and a workbook date system. A serial number by itself is not a universal timestamp, and a workbook does not provide a timezone merely because a cell looks like a date. The extracted XLSX preserves the readable format and the 1900 or 1904 date-system flag.
Raw CSV and JSON retain serial numbers. If you choose numeric-as-text, date serials become text in the new workbook too. Compare known dates after conversion, especially when combining data from different date systems. The tool does not silently normalize historical dates or assume an offset.
Use the supported bounds as a planning aid
Used ranges count empty positions inside the sheet rectangle as well as populated cells. A workbook with formatting applied far down a column can exceed the grid limit despite containing few useful values. Remove unused formatting or export a smaller workbook in the source application rather than expecting a partial extraction without notice.
Macros, encrypted files and complex visual objects need different handling. This tool rejects macro content and does not reproduce charts, pivots or the original print design. Its useful output is a bounded data package with visible decisions and a loss report, suitable for review before the next processing step.