Here are the access rights relative to Project Documents:
The only users who can unlock a locked document are Administrators and the Project Manager. Even the user who uploaded the document cannot unlock a project document locked by another user.
Any user who can access the project documents area in a project can download from any folder in the document tree.
Any user who can access the project documents area in a project can upload documents in any folder of the document tree.”
Administrators and project managers can delete an unlocked document, regardless of its location in the document tree.