There is quite a number of codepages from the DOS era. Perhaps the most popular was CP 850, for Western European languages. Quite some Microsoft software still produces such files; also, Unicode was initially rejected in the Far East, so we still find files in particular codings, generally known as CJK. You can try
enca to find how your file is coded.
But no, it is not possible to know how it was created in the first place.
VIM itself can read such files, as it can convert from a range of encodings when reading files for editing. This is done with the
++enc=encoding option to the
:edit command. So, for example, if you determine that the non-ISO 8-bit extended-ASCII encoding in question really is code page 850, this can be read into VIM with:
:edit ++enc=cp850 file.txt