They may be called Ulead Project or Preview Document UPD
They seem to be created when rendering to Mpeg type files, but not all renders get the treatment.
Not sure what they are used for, i think may be associated with Smart Render, but that's just a guess.
I delete these types without problems, if the system needs them it can create another.
I have not seen any changes or problems in deleting these UPD files.