With WordPress + Visual Composer, how to restrict a user to change some content in a page?

There is no such granular control. The only possible way around it is to use shortcodes that insert content from other “posts” and restrict the access to those posts.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)