Hmm, ok we I will give you the name and path of the jsp file that can be modified 

I will send you something shortly

If you are using AEM Forms OSGI you need to upload the templates and they will reside in the crx repository under content/dam/forms and documents folder they do not reside inside the web logicif you were using livecycle and the xdp are in workbench then they will be residing in the file system

The pdf viewers that come with the browsers are not Adobe products and as such they may not support all the features

You will need to configure the instance on which your workflow is running using the configuration manager on the publish instanceplease follow the his documentation and configure the AEM DS settinghttps://experienceleague.adobe.com/docs/experience-manager-64/forms/install-aem-forms/configure-aem-for...

Any rdbms database 

The output service is provided out of the box you can write a simple post wrapper as Shown in the link I sent earlier

https://experienceleague.adobe.com/docs/experience-manager-learn/forms/document-services/output-and-forms-services-article-develop.html?lang=en

Make sure you both are using Adobe reader / Acrobat

What kind of form is this?pdf or adaptive forms ?