My scenario is:
I have a doc type XYZ that permits to insert JPG DOC XLS and PPT.
These doc contains a workflow where occur approvals and rejections. After user "A" insert a file example.PPT file and changed status, this doc is sent to next user in this workflow. When user "B" access this doc, is possible insert a lot of DOC, PPT, JPG, XLS change status, but user "B" DON'T CAN CHANGE example.PPT (file inserted for 1st user in this process).
What's the best solution for this situation?