The only place to use the two phrases “in relation to” and “pertaining to” is an article about not using them. In most cases, these phrases can be replaced with simpler words such as ”about”, “for”, “on” or “in”.
Keep your writing clear and simple to allow readers to focus on your key messages. Unnecessary words and phrases just make it more difficult to focus on the important words.
Next time you read text with either of these two phrases, replace the phrase with “about” or delete it and see if the meaning changes. Avoiding “in relation to” and “pertaining to” makes the text clearer.