I think you need to attach contract documents (word, pdf etc.) to the activities in your project schedule, right?
Well you can do it by going to the WP's and Docs tab and inserting all the various documents that need to be attached in the schedule. Once done with it, go to the activities tab and assign the documents as required.
As of this writing Primavera Unifier does not support attaching files to individual activities. However there is the ability to attach a file to the Comments associated to Schedule Sheet itself. There is also the ability to define Scope Manager which links Business Process records to the individual activities, and in turn files can be attached to the linked BP record.