I received a doc file today, I can’t edit the table header - I get the error “It is impossible to change protected content. Changes will not be accepted”
Table - Remove cell protection not active, save as odt not help to me.
What should I do to unlock cells?
Sorry for my English skill and russian language screenshot
You might want to share the file (because protected content might be of very different nature, from document protection to fields).
Also you might want to ask that at https://forumooo.ru, or at #libreoffice-ru (FreeNode IRC) or LibreOfficeRu (telegram).
Another option to resolve this challenge it to simply drag and drop the locked items from the 1st Write document to a new Writer document. After this, all the items into the 2nd document will be unlocked.
Below is the same message as above. But with details if you’re interested in those.
Steps:
Open the first Writer document. The one which includes the locked items.
Open a second empty and fresh Writer document
Using the first Writer document, select all the items. Including the locked ones.
Click, hold, then drag and drop all those items all at once. In other words, drag and drop the whole shebang from the 1st document to the 2nd document.
Into the 2nd document, all items are now unlocked. Joy 
Save the 2nd document
Optionally, adapt the formatting of the 2nd document. So that it matches the 1st document.