A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Excel does not have a way to show you a forgotten workbook password, so there is nothing to look up inside the file.
First, work out what the password is protecting. If the workbook opens but you cannot edit or add data, go to the Review tab and see whether Unprotect Sheet or Unprotect Workbook is shown. You will still need the password to remove that protection, so try the passwords you commonly used when the file was created. Also check for an older copy of the file, or an earlier saved version of it, from before the password was added.
For the future, make a password that is long, mixes letters and numbers, and is not a word or date someone could guess. Keep it written down in a safe place that only you can reach, so you are not locked out of your own file again.