In order to run when the document is opened, the macro needs to be renamed AutoOpen and the document should be saved as macro enabled. However you cannot force the user to run the macro.
Code:
Sub AutoOpen()
Const strPassword As String = "password"
With ActiveDocument
If Not .ProtectionType = wdNoProtection Then
.Unprotect Password:=strPassword
End If
.Revisions.AcceptAll
.Protect Password:=strPassword, _
NoReset:=False, _
Type:=wdAllowOnlyReading, _
UseIRM:=False, _
EnforceStyleLock:=False
End With
End Sub