Apply Password Protection

Aspose.Slides

//Instantiate a Presentation object that represents a PPT file
Presentation pres = new Presentation();

//Setting Password
pres.getProtectionManager().encrypt("pass");

//Save your presentation to a file
pres.save("data/AsposeProtection.pptx", com.aspose.slides.SaveFormat.Pptx);

Download Source Code

Many more examples are available at Aspose Docs.