Fill document variable with filled in field?

Hello,

We would like to create and send a document using Sign that automatically changes a variable in the document's text depending on the value that has been filled in by a recipient.

So an example would be:

We send a document that starts off with the text "Dear [COMPANY NAME]".

At the top of the document, a text field asking for the signer's company's name will be available. Once the signer fills in their company name (for example: HelloWorld Corporation) the document automatically adjusts the variable in the text to their company name "Dear HelloWorld Corporation".

We've seen this being used before. Can someone please explain how to do this?

Thank you very much!