External data sources integration using JDBC

What do you mean by "third party"? Is the vendor not on the list of supported databases here: docs.appian.com/.../System_Requirements.html

Appian Cloud will not allow any "unsupported" JDBC connections, so if that's your situation, you'll likely need to look at using Web services to transmit data (i.e. some NoSQL vendors support REST APIs). On-premises, you can try configuring additional JDBC sources directly through the app server, but they are completely *at your own risk* and you won't get any support from Appian with them.

I identified a JDBC driver that can support share point integration. I did doubt that cloud customers may not be permitted for additional unsupported jdbc sources. I am more interested in learning the possibility for the following given situation. Let us consider on premise situation. If the driver provides list of documents by folder, would I be able to show them directly after saving them to meta tables in Appian business database in a grid, and open & edit a document using the link. Upon Save, my process model should write back the doc to Share Point for the same metadata parameters as different version. We are trying using Appian native a!shp.. but wanted to learn more about such kind of integration possibility.

SharePoint comes with a suite of services that you can call natively to update documents or lists. Depending on what version of SharePoint you are on you would need to use webservices or a RESTful approach.