ETZ does not have the facility to allow the agency to electronically sign a document but you can print the contract when signed by the client or contractor, then ask the agency to manually sign this document and upload to the signed document to the assignment using the following method.
Under Document management set up a new document called say Completed Document:
It does not matter what you select as - Action Required or Action By, but you must select to attach it to the entity (assignment), do not choose to upload a file at this stage.
Now on the entity (assignment) add the document but at this point you can now select to upload the signed document, but please also untick the option - Create document from available template:
Now select to manage workflow, but on this screen we are going to select to just - Set document workflow as signed but not selecting any other options: