Are There Cut-and-Paste Jobs in the New Testament? The Case of 2 Corinthians

How much of the early Christian writings consist of scissors-and-paste jobs, where later editors cut up earlier writings and stitched them together into one continuous work, so that what we have now are not the originals but only the final edited version?  Are there books like that, for example, in the New Testament?  In a recent post I mentioned how the early Christian writing called the Didache is that kind of thing, with three documents artificially combined into the 16-chapter book we now...