To really use and benefit with PowerPoint on an iPad, you will have to sign in with your Microsoft Account. So what is a Microsoft Account? It is essentially the email address that you use with Microsoft services such as Hotmail, Live.com, Xbox, etc. When you run PowerPoint for the first time on your iPad, you are asked to sign in – if you already did so at that point of time, then you need not do anything else now since you are already signed in. On the other hand, if you continued that time without signing in, you can choose to sign in at a later time.
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