2023-12-01.

Libreoffice 7.6.2.1 
Opening a form from a .doc (ms-word 2007?) format.
Annoying message on any attempt to change outside grey input-fields:
  "Read only content cannot be changed, no modifications will be accepted"

Here, 
 https://ask.libreoffice.org/t/read-only-content-cannot-be-changed-no-modifications-will-be-accepted/9506/7

one comment after many others, 

redN00ws, Aug '14
	Have you tried ‘Format’ > ‘Sections’ ?
	Then select the Section (eg. Section1) with ‘Write Protection’ activated and deactivate it.
	Now it should be editable…


This worked for our case. 

Note that the problem seems to come from importing messy alien file-formats in the first place.