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Lock or unlock specific areas of a protected worksheet
You can lock only specific cells and ranges before you protect the worksheet and, optionally, enable specific users to edit only in specific ranges of a protected sheet. Follow these steps: On the Review tab, select Unprotect Sheet (in the Protect group). Select Protect Sheet to change to Unprotect Sheet when a worksheet is protected.

Restrict changes to files in Excel - Microsoft Support
On the Review tab, in the Protect group, review the following protection options: Protect Sheet Protect the worksheet and contents of locked cells. Protect Workbook Protect the workbook for structure and Windows.

Protect a worksheet - Microsoft Support
Worksheet protection is a two-step process: the first step is to unlock cells that others can edit, and then you can protect the worksheet with or without a password. Step 1: Unlock any cells that needs to be editable. In your Excel file, select the worksheet tab that you want to protect.

Lock cells to protect them - Microsoft Support
Follow these steps to lock cells in a worksheet: Select the cells you want to lock. On the Home tab, in the Alignment group, select the small arrow to open the Format Cells popup window. On the Protection tab, select the Locked check box, and then select OK to close the popup.

Protection and security in Excel - Microsoft Support
Excel gives you the ability to protect your work, whether it’s to prevent someone from opening a workbook without a password, granting Read-Only access to a workbook, or even just protecting a worksheet so you don’t inadvertently delete any formulas.

Protect a workbook - Microsoft Support
Add a password to protect your entire workbook and control whether others can open or make changes to it. Protect your file by setting passwords for Open and Modify.

Video: Restrict changes to files - Microsoft Support
Use read-only protection and passwords to prevent other people from opening or modifying documents. Open the document that you want to make read-only. Select File > Info. Select Protect Document > Mark as Final. Note: In Excel, select Protect Workbook. In PowerPoint, select Protect Presentation. Select OK.

Display or hide formulas - Microsoft Support
On the Protection tab, clear the Hidden check box. Make cells display the formulas they contain, instead of the formula results. Protect cells so that formulas cannot be displayed or changed.

Why do I get an "Unprotected Formula" message in Excel?
By default, all cells are locked to protect them from accidental or unauthorized changes. In this case, the cell containing the formula is not locked for protection. Resolution. Lock the cell by doing one of the following: Select the Error Checking button next to the cell, and then select Lock Cell.

Protect controls and linked cells on a worksheet
To prevent users from changing the protections on the cells and controls that you have set, protect both the worksheet and the workbook. For more information, see Protect a workbook.

Restrict access to workbooks with Information Rights Management in ...
Select Protect Workbook, point to Restrict Permission by People, and then select Restricted Access. In the Permissions dialog box, select Restrict permission to this workbook , and then assign the access levels that you want for each user.