In preparing your talk you need to decide whether you are to present with a full script, notes or from memory. This depends on the occasion and purpose of the presentation but which ever method is chosen, it is always acceptable to refer to your fuller notes if needs be during a presentation.
Notes on cards or on slides/ flipcharts can be used as memory joggers if you present without notes. If you are required to read a paper, at least be able to look up occasionally . Remember that failing to prepare is preparing to fail.