Thanks for your inquiry. I am afraid it is not possible to restrict download of a document using Aspose API. As API is class library and does nothing with GUI/Viewer, Save/Save As options are not a feature / property of PDF document but these are the features of the Tool / Viewer which is used to display the PDF document and Aspose.Pdf can only manipulate the PDF document and not the PDF Viewer /Tools.
We are sorry for the inconvenience.
Adding more to Tilal’s comments, in order to view/display PDF files, you may consider using ViewerApp of our sister company named GroupDocs, as this application provides the feature to restrict PDF downloading.
Please note that our [EULA]
(http://www.aspose.com/corporate/purchase/end-user-license-agreement.aspx) is displayed using ViewerApp and as you can notice, there is no save option to download the file.