I receive documents for signing and cannot replace my signature

My organization does not own Adobe Sign. 

However, we do use Adobe DC pro. 

I have two problems:

1. I receive documents that other people signed via Adobe sign - and then I cannot certify them with my digital signature on Adobe DC. It is locked and no option to add anything. 

2. When I ask them to send the document through Adobe Sign, it uses an old signature file and there is no way for me to replace it. 

Basically I cannot sign electronically files when someone used Adobe Sign. 

This is not encouraging if we want to consider Adobe Sign as a service. 
What to do?

Thanks