Hi @yoko_ishioka ,
Nice to meet you.
I have a solution for you if you’re willing to try out our app. We have an App on the HubSpot Marketplace called Portant. We have built it to be simple and tightly integrated with HubSpot. It takes information from Deals and associated objects, like contacts** and generates custom documents, which can be sent to be signed. You can check it out here:
Also, I am happy to hop on a call to help you get set up 
Just reply to this message or send me an email here james@portant.co
Please let me know if you have any questions.
Cheers,
James