A certificate of existence show only that, that a company exists. The articles of incorporation show what the company can and cannot do within the law.
Articles of Incorporation have become looser over the years and now often state that the company can do all it likes to achieve a profit or indeed in more recent times all it believes will enable it to achieve that end.
The articles will however tell you how many officers a company should have and the like which is often usful information for making sure that you understand the structure of the entity and showing that you "know your customer".
Compliance Officer Association, Privacy Officers Association, AACFE,MICM,SHRM.