It is possible to lock your cells to prevent people from changing the contents but you must protect the worksheet in order for the locked cells to work.
By default Excel locks (protects) all cells and charts but the protection is disabled until you choose
It is possible to lock your cells to prevent people from changing the contents but you must protect the worksheet in order for the locked cells to work.
By default Excel locks (protects) all cells and charts but the protection is disabled until you choose (Tools > Protection > Protect Sheet).
There is a whole range of specific editorial actions to occur even on a protected sheet. You can also allow users to sort, use Auto Filter and Pivot table reports.
You can also allow password access to specific cell ranges (Tools > Protection > Allow users to Edit Ranges).
What will it Protect?
It is possible to protect individual cells from being modified, resized, moved or deleted.
When you protect cells this is down via the (Format > Cells) (Protection Cells). By default, the cell protection attribute is set to Locked. If you protect a worksheet then every cell is protected. You must turn off the locked attribute on every cell that you want the user to be able to edit.
Protection of workbooks and worksheets can easily be hacked using simple VBA macros.
It is possible to force your users to Enable macros when they open a file. Basically have a message box that appears by default saying that nothing will run unless you enable the macros. If macros are enabled then do not display this dialog box.
Another possibility might be to include an expiry date. Although the draw back of this is that you can change the system clock on your computer. Alternatively allow them to open a file a fixed number of times.
UnProtecting Individual Cells
When you protect a worksheet all the cells are protected by default although it is possible to remove this protection.
Removing this protection from individual cells and ranges can be done using the (Format > Cells)(Protection tab).
You cannot change these properties once the worksheet has been protected.
You can change the protection for individual cells by highlighting the cells and selecting (Format > Cells)(Protection tab).
Locked - Remove if you want the cell(s) to be edited after the worksheet has been protected.
Hidden - Prevents any formulas in the cell(s) from being displayed in the Formula bar after the worksheet has been protected.
You can change the exact aspects of the cell protection by selecting (Tools > Protection > Protect Sheet)
Excel does not provide any on-screen indication