A complex Excel 2007 workbook could require multiple sheets. By default, Microsoft provides three sheets on each workbook, but you can add as many as you need.

For an individual spreadsheet, select Protect Sheet followed by Unprotect Sheet to remove password protections. For a workbook composed of multiple spreadsheets, select Protect Workbook followed ...

You can sum cells across multiple sheets in Excel. This article presents steps for Adding single-cell values or Adding values in the range of cells.

You worked hard to put that Excel sheet together, now protect it from unintended damage.