Seems strange that you are going to delete document that can be changed during the operation.
But even in that case the read operation is done once and the newly created document will have the content at this moment. No transaction needed.
And if youare expecting the write operation in the result document... all of the content will be overwritten.
Generally, make sure, that you are not working with actively used documents. Otherwise a whole bunch of errors can happen: loss of data, update of non-existing documents and so on. Or... change the functions to handle all the cases: only copy, but not move and create the new doc at least with merge option, but better check if the doc exists and merge the data with some custom logic.