Electronics Repair Questions? Ask an Electronics Technician
You can press the REC button whilst recording to pause the recording, then press the REC button again to continue to recording. This is the only way to add to a file whilst recording - you cannot add to it if you have already pressed STOP.
To concatenate recorded files on the PC, you can use the simple free online tool: https://audio-joiner.com/
or you could use one of the many free merging programs available for download: https://www.shchuka.com/software/mergemp3/
Let me know if you have any further questions on this :)