The only program capable of reliably recovering .xlk files would be Excel, the very program that generated the backup in first place. Once recovered, the spreadsheet can be saved to any of the available formats, including the standard XLS format.
Convert Microsoft Excel backup file to Microsoft Excel 97 to 2003 workbook.
We found 2 software records in the database related to .xlk to .xls file format conversion.
Microsoft Windows software - convert xlk to xls on Windows
A popular spreadsheet application distributed with Microsoft Office suite
Convert from xlk file format
|Yes, Microsoft Excel supports xls file conversion as a target file type.||Yes||Yes||xls editor||Yes||No||No||No|
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned xlk to xls. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert xlk to xls on OS X
A popular spreadsheet application from the Microsoft Office suite