ActiveX Installs must be configured for proper restriction in PowerPoint Viewer.
Microsoft ActiveX controls allow unmanaged, unprotected code to run on the user computers. ActiveX controls do not run within a protected container in the browser like the other types of HTML or Microsoft Silverlight-based controls. Disabling or not configuring this setting does not block prompts for ActiveX control installations and these prompts display to users. This could allow malicious code to become active on the user's computer or the network.
Set the policy value for Computer Configuration -> Administrative Templates -> Microsoft Office 2016 (Machine) -> Security Settings -> IE Security "Restrict ActiveX Install" to "Enabled" and 'pptview.exe' is checked.