The following VBScript code can be used inside a "Run VBScript" Action, in order to open a password-protected Excel document.

Set xl CreateObject("Excel.Application")
Set wb xl.Workbooks.Open("%Excel%",,,,"%PasswordtoOpen%")
xl.Application.Visible True

- Notes

%Excel% -> Variable that contains the Excel file path

%PasswordtoOpen% -> Variable that contains the Password

After opening the Excel, the "Attach to Running Excel" Action can be used in order to go on with the Excel processing using the Excel Actions.