Thanks for inquiring Aspose.
I have observed your requirements and regret to share that Aspose.Slides and Aspose.Cells generate the presentation and excel files programatically and there is no viewer associated with them in API.
However, you can encrypt the presentation and excel file while saving. Please visit documentation link, Encrypting with Aspose.Cells and Saving Presentation File for your kind reference. Please observe, setWriteProtection() method in PresentationEx API reference guide page to set the presentation password.
I hope the shared information will be helpful.