Comparing two documents and return the matching Score(Signature Matching)

What have you tried so far?

Two options for you to try,

1. Use the Apryse WebViewer Component Plug-in. It features document comparison in semantic categories. The score percentage is something you will have to work out depending on outputs I think. 

2. Appian RPA has Image Recognition capabilities. Explore and build a bot to do the comparison and return score. 

I would suggest to explore Apryse first as that seems more promising to fulfill your usecase and easier to implement too. Hope it helps!