Any custom spelling dictionary that you create within PowerPoint or any other Microsoft Office program is used by all the Office applications installed on your computer. Also, any changes made to the list of words within a custom dictionary reflect in proofing tools of all Office applications. Each logged-in user has a default custom dictionary called RoamingCustom.dic, stored in a separate folder for each local user. So, what exactly is a default dictionary?
Learn how to disable, enable, and set the default custom dictionary in PowerPoint 365 for Windows.