I’ve tried your sample code to save the presentation to a stream from here: https://docs.aspose.com/display/slidesnet/Saving%2C+Printing+and+Managing#Saving,PrintingandManaging-SavetoStream
I’m using this in an ASP.NET Core web app. What i found is, without adding toStream.Position = 0; it wouldn’t download. This took me a lot of time figuring out, so I think you could add this to your docs.