A certificate is a document that proves that you have completed a course, program, or event. It also includes the date, your name, and the name of the organization that ran the event. An acknowledgement is a statement that recognizes something or someone. It is usually given in the form of a letter, but it can also be given verbally. For example, an acknowledgement can be given to a donor, an employee, or a volunteer. It is a way of saying "thank you" for the contribution that the person has made.