Software on this site can’t help you with the password to open documents, it removes the other passwords in Excel, not the password to open. But there are other solutions:
Check out Excel Key.
If the file is the new Excel format (.xlsx/.xlsm) password removal cannot be guaranteed as Excel now uses strong 128-bit AES protection.
If the password is short, simple or uses a limited set of characters, password removal is probable.
For .xls files password removal is guaranteed.
For old 97/2000/XP/2003-files (.xls) I can also recommend this one: Excel Password Recovery Lastic