That depends on what level of protection you need. If the Excel file has a workbook password to even open and read, then no, that won't fly.
Consider removing the workbook password and use sheet protection instead. People will be able to use formulas that reference locked cells on a protected sheet. If they open the workbook they will not be able to make changes to locked cells on the protected sheet.
If you don't want them to even see data when they open the workbook with the protected sheet, there are a few ways to handle that. If you need help with that, please pipe up.
Edit after comment: here are a few suggestions
- hide the lookup sheet. Vlookup works with hidden sheets
- insert a few empty columns to the left of the lookup table, so the lookup table is no longer visible on the screen. Format all cells as "locked" and protect the sheet, untick the option that allows selecting locked cells.
- format all cells with custom format
;;;, which will not display anything in the cells. Lock and protect as in the previous step
Note that a savvy Excel user will be able to work around these steps. Sheet protection is meant to prevent inadvertent changes, not malicious intent.