Get [Document|WorkBook.Worksheets].CustomDocumentProperties[propertyName] // returns a DocumentProperty
However in Slides for both Presentation and PresentationEx you have to use the DocumentProperties class directly and it is basically just setting/getting a type Object. Funny enough, it does have a Remove method.
What's the reasoning behind this? I'd expect that the API for CRUD on custom properties would be the same across Office documents at least. It seems a simple thing to implement on Aspose's end and would save me the bother of creating my own wrappers.
We really appreciate your feedback and thank you for highlighting the issue. Our development team is looking in to the issue and hopefully in the next major release of Aspose.Slides for .NET, the uniform feature support for common features will be provided.
The support for adding, accessing, finding and removing custom document properties has been provided in Aspose.Slides for .NET. Please visit this link for your further kind reference. As far as the issue of uniform manner of setting custom document properties in Aspose.Slides as in case of Aspose.Words/Cells is concerned, an issue with ID 30455 has been created in our issue tracking system for this. Please share with us, if you still face any issues.