If it is from an unknown source, I strongly advise deleting it to prevent potential security issues.
This is an older Excel Spreadsheet format (Excel 97-2003). It will open in modern Excel versions, but may trigger compatibility warnings.
If you cannot view the contents, you may need a password from the original sender. To help you better, could you tell me: Where did you download this file from?
was the file supposed to contain (e.g., a report, data list, invoice)?
Before opening any .xls (Excel) file, scan it with antivirus software (e.g., Windows Defender, VirusTotal ).