The best option is to open it using Adobe PDF viewer. Previously browsers would allow Adobe PDF viewer to be the default PDF viewer, hence you may not have had this problem
I just tried the form you provided in the link using Acrobat and it works fineis it happening when you open the form using the pdf viewer of the browser?
you can prevent some authors from accessing the rule editor. you cannot prevent people from accessing the rule editor and not making changes https://experienceleague.adobe.com/docs/experience-manager-learn/forms/adaptive-forms/restricting-rule-editor-aem-forms-technical-video-use.html?lang=en
Exactly, you can write custom code to store the generated pdf in s3 to start I would suggest storing a sample pdf in s3 using Java codeif that is working, convert that code into custom workflow component and use it in your process