How communication is enabled in multiple different network using different routing protocols

The optimized way to accomplished this task is by redistribution of route please check restribution of route concept . We have fesabilty to export and import route in different routing protocols for example if ospf and static routing to communication redistribution has to be configured in border switch

Assuming you are having cisco layer3 switch connecting two different network in his layer3 switch redistribution of routes can be configured between static and OSPF route ensure advertising OSFP route into static route and static route in ospf

Router1(config)#router ospf 78 Router1(config-router)#redistribute static Router1(config-router)#exit Router1(config)#end

Likewise we can redistribute route from and to vice versa between different routing protocols

Unless you have multiple paths to the other organization, you don't need to run a routing protocol with them. You can use a static route to route traffic over the point to point link, and the other organization can do the same.

One of the assumptions of OSPF is that all routers are trusted. In your case, the routers of the other organization should NOT be trusted, so OSPF is not a good choice. If you had to run a routing protocol, BGP is a better choice, but it doesn't seem to be necessary in your case.

Generally, BGP is an appropriate routing protocol for inter-domain / inter-network signaling. It has features intended for networks which are under different administrative controls.

OSPF is not appropriate for your intended use. Don't do that. OSPF is categorized as an Interior Routing Protocol specialized at distributing routing information within one network under the control of a single organization.