Convert an XLSX Workbook to Older XLS

Before converting, ask whether the receiving system accepts XLSX, CSV, or a smaller data extract. XLSX is the normal modern workbook format, whereas XLS uses an older binary representation. Moving backward may constrain worksheet dimensions and features. A workbook that relies on large datasets, modern formulas, rich formatting, or newer chart behavior may not translate cleanly. If the receiving system only needs rows and columns, a carefully reviewed data export may be safer than pretending the whole interactive workbook can be preserved.

List the relevant sheets and the exact cells the recipient will use. Check formulas separately from their displayed values, and verify totals after opening the XLS in the target application. Be alert to date serials, long identifiers, decimal separators, and characters outside a legacy application's expected encoding. Conditional formatting, validation rules, and named ranges may need manual review. Compare row and column counts before and after export; a valid file can still omit content if it exceeds the receiving format's practical limits.

A file called report.xls that still contains XLSX bytes would be a broken download. Keep the XLSX master because it is the best source for later edits and for investigating loss. No promise is made about macros, recalculation, or exact visual identity. If this is added later, real downloads should be checked in the intended legacy environment as well as a modern reader.

Choose an acceptance sample from the source: one formula, one long identifier, one date, and one styled cell. After saving as XLS, reopen those cells in the recipient's intended application. If a value changes, the route should warn rather than label the download a success. Compare sheet dimensions too, because a backward export may silently truncate an oversize table.