Hatti you are fortunate apparently not to have a file size limitation.
Tomasc had the right answer. Use DOS to join the two files. But work on the original files copied from the camera, as he said in one of his replies. Do not process each file first with PD16 to produce two mp4 files, and then try to use DOS on the MP4 files - this does not work.
The old simple solution is best. No complicated hard to understand modern software! Thank you so much Tomasc! : A bonus for you!
Thanks again
David David Pentecost