How do i unprotect a document (Toggle ReadOnly/Edit Mode)

I want to edit a table of contents.
To switch off Write protect, Help says
Use the Edit File icon to activate or deactivate the edit mode.
Could someone please tell me where to find the Edit File Icon?
Thanks

Misleading title: it is not about unprotecting a document, but only its table of contents.

Concerning files opened “read-only”
The icon for toggling between ‘Locked’ and ‘Edit’ mode seems to no longer be shown by default.

  1. You may use the menu path > ‘Edit’ > ‘Edit Mode’
  2. By default the shortcut Ctrl+Shift+M should do the toggling.
  3. You can customize a toolbar to show the icon again. For the ‘Standard’ toolbar you only have to click the checkbox left of the already contained command ‘Edit Mode’ to get the icon showing again. Strat with > ‘Tools’ > ‘Customise…’.

Edit with respect to the comment below.
I obviously had missed the point of the question.

A table of contents should be locked as it has to mirror the state of the document when the TOC was created. It has a context menu (rightclick into its area) that offers

  • to ‘Update’ the TOC,
  • to ‘Edit’ its settings (not the text)
  • to delete it.

The ‘Edit Mode’ applicable to documents opened read-only is not applicable to a TOC.

Thanks for your advice. I use an Apple Mac computer. When I click on ‘Edit’ >‘Edit Mode’ Edit Mode is greyed out.
Using Ctrl+Shift+M highlights Paste in the Edit Menu. Any further suggestions would be appreciated.

Please ignore my earlier comments. I’ve solved the issue.
Once again many thanks.