1)How PDC is different from AES and what are the benefits of using this? 

AES and PDC both provide good capabilities for Pega Platform application governance, monitoring and production support, but PDC is better software with better support and a better price.

Better Software:

The most current AES application version is AES 73. It was released Q4 2017.
The most current PDC service version as of today is 2.05, which was released two days ago. PDC is enhanced every week or two. See https://community.pega.com/knowledgebase/release-note/whats-new-pega-predictive-diagnostic-cloud

There is likely going to be an AES 83 available Q1 2019 but PDC will always be have more features / better insights than AES since it is enhanced on weekly basis while AES releases take months to package and test.

Better Support

By default, your PDC tenant(s) are configured so that Pega Support and the PDC team can collaborate with you. If you allow it, you can engage with Pega to help understand what PDC is showing, and PDC team can quickly evaluate  any issues and quickly turn around bugs or enhancements as appropriate - plus we have access and responsibility to address operations issues. We intend in the future to offer a one-click option to engage Pega support on issues that have been identified in PDC improvement plans.

Better Price

The PDC service is free for all customers. There is no license to use PDC. Regardless of your license cost for AES, PDC will cost you less as you do not need to pay for application server hardware / virtual servers, database software license, web app server license and maintenance, data center operations staff costs, Pega platform administration to host AES, etc.

2)How the SOAP configuration will be done and what type of PEGA Soap request needs to be mapped, to send response data to PDC.

From designer studio, go to system / settings / PDC and plug in the unique URL of your PDC tenant service endpoint (which you can get from the Welcome screen when you log into PDC from a browser). 

That's all the configuration needed in Pega Platform itself. Within Pega there is a combination of custom engine code to process alerts and health status messages (soapAppenderPega) and agent-driven connect-REST / connect-SOAP but they all take the one base URL that you enter on the landing page. 

You will most likely need to configure your JVM's to use a proxy server (quite common for data centers to block direct public internet access)  and proxy server might need to whitelist the PDC service DNS name / hosts. Some application servers also require that a system administrator download and install the PDC service SSL certificate.

3)Do we need license to use it. What about 90 Days Trial version (if any)?

No license. Use it forever

3-a If Any Maintenance/Upgrade will be required on regular intervals?

We periodically enhance the "PegaAESRemote" rules that run in your system to push PDC information about system health and operating environment as part of building better features for PDC. For example, we have an agent that tells PDC agent queue state, so PDC can help diagnose and support agent operations, but we don't have comparable data for queue processor state, so we will enhance PegaAESRemote to gather queue processor statistics (pega 8) and push them to PDC. We will announce new rules on PDN and we are working to build a process to notify all PDC event subscribers about features or service issues.

At present, you need to download new PegaAESRemote rules to leverage new features. We distribute PegaAESRemote as a hotfix today via SR process but our next releases will be posted on exchange so you can download at any time.

4)How long it will take to configure the setup and any if step-by-step document available for the same?

If you are connecting a sandbox / play system with full internet access to PDC, and the system has a unique and meaningful name, all you need to do is go to system / settings / PDC and paste the URL.  Literally 30 seconds.

If you need to rename your system, go to system /setttings / system name and restart your system. Add time for system restart.

If you are in data center and need to configure proxy server, import certificates, update whitelists, etc it can be a lengthy process but there's nothing unique to PDC about that - its the same process you would need to use any cloud service from your java server stacks.