For some stupid reason, you may be required to write a stupid Word document by editing a stupid .dotx template. Even you are supposed to change some part of the stupid template, you may get the following stupid error:

You can't make this change because this selection is locked.

There are several proposed solution for this stupid problem but only one of them worked for me. 1

1️⃣ If your Word is missing Developer tab at the top, first go to Options → Customize Ribbon. and enable the Developer option.

Developer Options

2️⃣ Then click Design Mode to remove the stupid restriction.

Design Mode

3️⃣ Thank LaTeX developers.