An old XLS file has not been successfully migrated merely because it opens. Check a copy against recorded reference values before replacing the original or using the new file for real work.
Preserve the original and a reference
This guide concerns Excel 2000 workbooks tested in a current desktop spreadsheet application. Keep the original unchanged and work in a separate folder. Record filename, size, modification date and known application version. XLS is ambiguous: Microsoft distinguishes Excel 97–2003 and older Excel 5.0/95 formats sharing this extension.
If the old environment is available, record sheet names, important totals and dates, and print previews there. Include hidden sheets, macros and required add-ins. Use an isolated environment for old software, not your normal internet workstation.
Open the copy under controlled conditions
- Use File → Open in the target application. Record its exact version and all import or repair messages. Current Excel opens Excel 97–2003 files in Compatibility Mode; LibreOffice Calc can also open XLS files.
- Do not enable unknown macros or initially update external links. Record these dependencies separately. A displayed cached formula value does not prove that recalculation works.
- Compare sheet counts and names, selected formulas, totals, dates, decimal places and leading zeros. Check charts, named ranges, hidden content and print areas where used. Record differences with sheet and cell address.
- Test a representative calculation only in the copy: change a known input and compare the result with an independently expected value. Without a checkable reference, leave this test unresolved; do not approve the entire workbook indiscriminately.
Choose the target format deliberately
Save under a new name. XLSX cannot store VBA macro code; XLSM is one option when Excel macros are required. The extension does not guarantee functionality. LibreOffice and Microsoft Office cannot generally run each other’s macros unchanged. Required automation needs a separate functional review. CSV and PDF do not fully replace a workbook containing formulas, multiple sheets and features.
Check again after saving
Close and reopen the test file. Repeat the important value and print comparisons. Record the original, target format, application version, tested cells and remaining differences. Release the new file only after functional acceptance; retain the original and comparison evidence. If it fails, discard only the test copy and start again from a fresh copy of the original.