Yes.  Add the Opportunity as a Related Item - Open the Contract record > select the 'Related Items' tab > click Add Related Item > search for the Opportunity record > tick the checkbox > Click Add.  

(If you start with an Opportunity record and use the Copy Document functionality to generate your next transaction document and keep using Copy Document until you generate a Contract, the original Opportunity will automatically appear in the Related Items tab on the Contract.)

Tip: An easy way to find records is to search with the object reference.  The object reference can be viewed in a few ways:

• Hover over or open the Additional Information icon in the top right of the screen.
• On a landing page.  Simply add the Object Reference column to the list of displayed columns.
• Write a Report that displays the Object Reference column.