Yes, agree with you, we can use “COPY *.txt file3.txt” to do that. The challange is: if tens of files will be combined, the file order is a problem. In Emeditor, there’re UP and DOWN button available, we can move up or move down as requirements. But “COPY *.txt file3.txt” will do by default order (I guess it is according to alphanumber ascending of file name).
Of course, we can use “COPY file3.txt + file1.txt+file9.txt file3.txt……”, but we need more efforts.