Contract Document records can be sent out for Approval on an individual basis.
Open the related Contract and go to the Documents tab, Click on the Document record you wish to send for Approval.
Fig 1 - Contract Document selection
This will open up the Document record in full screen rather than a pop up. You will see that the Document record now has its own set of sub tabs, one tab will be 'Approvals'.
Fig 2 - Contract Document Approval tab
The Document record will have its own Approval status.
This status is independent of the Contract record Approval status. A Contract record could have an Approval status of [Approved] but the document records linked to it could still have an Approval status of [Pending].
Fig 3 - Contract Document Initial Approval status
Click on the [...] icon on the top right of the record and select the option for [Submit for Approval]
Fig 4 - Submit for Approval
Define how you wish the Approval flow to progress
Select the relevant People / Approval Group using the drop down list
The selected values can be moved around to define the order by using box's at the end of each value via drag and drop