"Herewith, I have attached articles’ for your review." Is an apostrophe necessary?
The apostrophe isn't necessary.
Most generally an apostrophe following an "s" such as that in—articles'—indicates that the word is both possessive and plural (this is called plural possessive [sometimes called the plural possessive tense or form]). In the sentence:
Herewith, I have attached articles' for your review.
You are literally saying:
Herewith, I have attached the articles [has/ have] for your review.
This sentence lacks an object to which the "articles" relate therefore the—s'—does not work in this instance.
When an apostrophe precedes an s at the end of a word (like this: 's) the author is attempting to convey possession. Again, the sentence above lacks an object that we can relate the "articles" to so we can't use the—'s—form. However we can use this form if we said something like:
The article's source is dubious (sketchy) at best.
The sentence above refers to the source that the article originates from (we are literally saying: "The article has a dubious (sketchy) source."
Most commonly if a word ends in an "s" then the word is plural, this indicates that more than one of that particular object/ subject is present, for example:
The articles are attached.
This sentence indicates that there is more than one "article" the author is going to attach.
As for your sentence the "articles" are neither plural possessive (articles') nor possessive (article's). There are numerous "articles" however so this makes "articles" plural and thus we don't need to add an apostrophe to "articles" thus your sentence should read:
Herewith, I have attached the articles for your review
I hope this helps some!