Assembly: Microsoft.Office.Interop.PowerPoint (in Microsoft.Office.Interop.PowerPoint.dll)
The collection doesn't include open add-ins, which are a special kind of hidden presentation. You can, however, return a single open add-in if you know its file name. For example Presentations("oscar.ppa") will return the open add-in named "Oscar.ppa" as a Presentation object. However, it is recommended that the AddIns collection be used to return open add-ins.