Frequently asked questions - Calc
Is it possible to open a password-protected Excel file in LibreOffice?
One might expect this to be impossible to do directly: this file cannot be opened by LibreOffice Calc unless you know the password in the original application.
However examples seem to show that the protection of .xls or .xlsx files sometimes only works within MS Excel. It depends on what type of protection, e.g. some workflow related password protection is not supported.
If the file is stored encrypted with a password then you do need the password to be able to open the file in LibreOffice.