Secure PowerPoint Presentation using Password Encryption in C#. The step by step guide on this gist is here https://kb.aspose.com/slides/net/how-to-secure-powerpoint-presentation-in-csharp-net/.

Secure PowerPoint Presentation using Password Encryption in C#.cs

using System;
//Install Aspose.Slides for .NET NuGet package 
//and then utilize the following namespace to
//secure PowerPoint presentation
using Aspose.Slides;
using Aspose.Slides.Export; 

namespace SecurePowerPointPresentation
{
    class Program
    {
        static void Main(string[] args)
        {
            //Set Aspose license before securing PowerPoint presentation
            //using Aspose.Slides for .NET
            Aspose.Slides.License AsposeSlidesLicense = new Aspose.Slides.License();
            AsposeSlidesLicense.SetLicense(@"c:\asposelicense\license.lic");

            //create an object of Presentation class from Aspose.Slides namespace
            //and provide the PowerPoint presentation to secure in the constructor
            Presentation PowerPointPresentationToSecure = new Presentation("PowerPointPresentationToSecure.pptx");

            //specify the password with which you want to secure the presentation
            //this can be taken as input password from the user/admin etc.
            String PasswordForPresentationSecurity = "8ma2bzdqgo";

            //Encrypt or secure the presentation with the password using Encrypt method
            //with the help of ProtectionManager
            PowerPointPresentationToSecure.ProtectionManager.Encrypt(PasswordForPresentationSecurity);

            //Finally, save the output presentation secured with password
            //provide PPTX as save format 
            PowerPointPresentationToSecure.Save("PresentationSecuredWithPassword.pptx",Aspose.Slides.Export.SaveFormat.Pptx);
        }
    }
}