Protect All Sheets With One Password

1. Open the workbook.
2. Press Alt + F11 to open the VBA Editor.
3. Click Insert → Module.
4. Paste this code:

Sub ProtectAllSheetsWithOnePassword()

    Dim ws As Worksheet
    Dim pwd As String

    pwd = InputBox("Enter the password to protect all sheets:", "Protect All Sheets")

    If pwd = "" Then
        MsgBox "No password entered. Protection cancelled."
        Exit Sub
    End If

    For Each ws In ThisWorkbook.Worksheets
        ws.Cells.Locked = True
        ws.Protect Password:=pwd, _
                   DrawingObjects:=True, _
                   Contents:=True, _
                   Scenarios:=True, _
                   AllowFiltering:=True
    Next ws

    ThisWorkbook.Protect Password:=pwd, Structure:=True

    MsgBox "All worksheet tabs and the workbook structure are now protected."

End Sub

5. Close the VBA Editor.
6. Press Alt + F8.
7. Select ProtectAllSheetsWithOnePassword.
8. Click Run.
9. Enter the password once.

That will protect every worksheet and also protect the workbook structure so users cannot easily add, delete, move, rename, or hide/unhide tabs.

Important Distinction

Protect Sheet stops people from editing cells.

Protect Workbook protects the workbook structure, meaning tabs cannot be moved, deleted, renamed, hidden, or added.

For your purpose, you want both, and the macro above does both.

To Unprotect All Sheets Later

Use this companion macro:

Sub UnprotectAllSheetsWithOnePassword()

    Dim ws As Worksheet
    Dim pwd As String

    pwd = InputBox("Enter the password to unprotect all sheets:", "Unprotect All Sheets")

    If pwd = "" Then
        MsgBox "No password entered. Unprotect cancelled."
        Exit Sub
    End If

    For Each ws In ThisWorkbook.Worksheets
        ws.Unprotect Password:=pwd
    Next ws

    ThisWorkbook.Unprotect Password:=pwd

    MsgBox "All worksheet tabs and workbook structure are now unprotected."

End Sub

One More Security Note

Sheet protection prevents normal editing, but it is not the same as full file encryption. If the workbook contains sensitive information, also use:

File → Info → Protect Workbook → Encrypt with Password