Create a multi-doc proof with docs already in WF?

Hi,

We have a use case where we would like to create multi-page proofs with documents that are already in WF. I can create a single document proof from within Workfront using an exsisting file but don't get a "Create Proof" option when I multi-select files. I can upload multiple files if we create the proof from within the WF Proof application but we would prefer to use the files that are already in WF because the files are uploaded in an earlier step than the proofing and are used for multiple purposes. Am I missing an option somewhere or is it not possible to do a multi-file proof from within WF?

Thanks!!