You can protect paginated article against geometry modifications if your lock level is greater than 0, if the article you are trying to lock are not already protected, and if the page layer you are working on is not protected.

To protect single text element of an article, select all its linked frames.

To protect all elements of an article, select all of them (you can use Edit > Select > Article).

Now, perform the steps, explained in Protecting objects against modification.