Are these files actually HXN files? Or are they OBJ, DXF, etc…?
Files have “fingerprints” you can look at in a hex editor to find the beginning, the end, and/or various other content information of the file.
HXN files start with the ASCII letters “HEXA” and end with ASCII “EOF” as shown in my accompanying snapshot (my files also have 5 spaces [20h] following the “EOF” but since EOF stands for (E)nd (O)f (F)ile, they may be spurious characters. I removed the 5 spaces from one file and it opened in hex just fine).
A good reason to check this on your files is that it provides you with a “confidence check” that the files are probably intact and complete and that something else (which is more likely to be easily reparable) is wrong rather than the files themselves being damaged.
Click thumbnail to see full-size image