Make sure you have the right Dropped Files options checked to enable dropped files to be created as Revisions.
Tools – Options – Dropped Files Tab – Confirm check in action before continuing
Tools – Options – Dropped Files Tab – Display a data entry form when creating a new Records
The Check In Document box will then pop-up when you drag and drop. You can then attach your document or pdfs as the latest Revision, thereby keeping the complete history of a document development and approval within a single record.